Video copy protection process enhancement to introduce horizontal and vertical picture distortions

ABSTRACT

Enhancements to a video anticopying process that causes an abnormally low amplitude video signal to be recorded on an illegal copy. The enhancements in one version introduce into the overscan portion of the television picture, just prior to the horizontal or vertical sync signals but in active video, a negative going waveform that appears to the television receiver or videotape recorder to be a sync signal, thereby causing an early horizontal or vertical retrace. One version provides (in the right overscan portion of the picture), a checker pattern of alternating gray and black areas which causes the TV set on which the illegal copy is played to horizontally retrace earlier than normal in selected lines with a consequential horizontal shift of the picture information on those lines. This substantially degrades picture viewability. In another version a gray pattern at the bottom overscan portion of the picture causes vertical picture instability. In another version selected horizontal sync signals are narrowed, causing irregular vertical retraces. Also provided is apparatus for removing or attenuating these enhancements from the video signal, to allow copying.

This application is a division of application Ser. No. 08/062,866, filedMay 17, 1993, pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Enhancements to a video anticopy process, the enhancements causingadditional degradation to the picture quality when a copy of a protectedrecording is played back, and additionally which reduce the viewabilityof unauthorized recordings of the protected recording.

2. Description of the Prior Art

Video anticopy processes are well known. An example is Ryan, U.S. Pat.No. 4,631,603 issued Dec. 23, 1986, incorporated by reference whichdiscloses (see Abstract):

"A video signal is modified so that a television receiver will stillprovide a normal color picture from the modified video signal while thevideo tape recording of the modified video signal produces generallyunacceptable pictures. This invention relies on the fact that typicalvideocassette recorder automatic gain control systems cannot distinguishbetween the normal sync pulses (including equalizing or broad pulses) ofa conventional video signal and added pseudo-sync pulses. Pseudo-syncpulses are defined here as any other pulses which extend down to normalsync tip level and which have a duration of at least 0.5 microseconds. Aplurality of such pseudo-sync pulses is added to the conventional videosignal during the vertical blanking interval, and each of saidpseudo-sync pulses is followed by a positive pulse of suitable amplitudeand duration. As a result, the automatic gain control system in avideotape recorder will make a false measurement of video level whichcauses an improper recording of the video signal. The result isunacceptable picture quality during playback."

Column 2, beginning at line 5 states that the added pulse pairs (eachpair being a negative-going pseudo-sync pulse followed by apositive-going "AGC" pulse) cause an automatic level (gain) controlcircuit in a videotape recorder to erroneously sense video signal leveland produce a gain correction that results in an unacceptable videotaperecording.

Therefore this prior art "basic anticopy process" causes an abnormallylow amplitude video signal to be recorded when a copy is attempted. Someof the effects observed when the illegal copy is replayed are horizontaltearing (positional displacement) and vertical displacement of thepicture. Whether this occurs or not is often largely dependent on thepicture content, i.e. presence of white (light) and black (dark) areasin the picture. Therefore this prior art process, while generallyproviding excellent copy protection, with some combinations of videotaperecorders (such as VCRs) and television sets provides a picture viewableby persons willing to tolerate a poor quality picture.

Also, with certain VCRs and TV sets the various well known prior artcopy protection processes provide little picture degradation. Certainmarkets for prerecorded video material have a high rate of piracy, i.e.illegal copying of videotapes, in spite of copy protection and theseviewers apparently are relatively insensitive to the poor qualitypicture in illegal copies caused by the prior art copy protectionprocesses. Thus there is a need for copy protection process enhancementswhich degrade the quality of the picture even more than that of theprior art processes.

SUMMARY OF THE INVENTION

In accordance with the present invention, the above-described prior art"basic" copy protection process is enhanced by further modifying thevideo signal in several ways to ensure that the necessary picturecontent requirement is met to maximize effectiveness of the basic copyprotection process.

The further modifications include blanking a portion of the active videoin the overscan area of the picture just prior to the occurrence of the(1) horizontal or (2) vertical synchronization (sync) signals, andinserting into the blanked portion a waveform that (for a video signalhaving reduced amplitude) is perceived by the TV receiver or videotaperecorder as a sync signal, and so causes incorrect synchronization ofthe VCR or TV receiver. Using this modification especially only oncertain video lines or fields causes substantial picture degradation ofan unauthorized copy. Another modification narrows the horizontal syncpulses to cause sensing of a spurious vertical sync signal in a TV setand will also affect certain videotape recorders.

In the horizontal modification, the right edge of the picture isreplaced by a "checker" pattern appearing (like a checker board) ofblack and gray rectangles. The width of this checker pattern is chosento be within the overscan (not viewed) part of the picture whendisplayed on a standard television receiver. It will be understood thatwith an abnormally low signal amplitude, when the picture content islight (such as mid gray), the left edge of the black rectangle incertain video lines will trigger an early horizontal retrace as being anegative-going (towards blanking level) transition. When the picturecontent is dark, the right edge of the gray rectangle (adjacent to adark picture area), in certain video lines will trigger an early retraceon each line as also being a negative-going transition. (The descriptionof video waveforms herein follows the convention of positive amplitudebeing white and negative amplitude being black).

The horizontal modification checker pattern in one embodiment isgenerated at a rate slightly asynchronous to the video field repetitionrate, so that the checker pattern appears to slowly move up or down thepicture, at a rate of about 1 second for any given point to migrate fromthe bottom to the top of the picture or vice versa. The checker patternhas no effect on the picture when an original (authorized) cassette isreplayed since no signal conditions are present in the TV set which arein any way abnormal.

However, when an illegal (unauthorized or pirated) copy of the cassetteis replayed using a videotape recorder, the signal attenuation resultingfrom the above-described prior art copy protection process, incombination with the checker pattern, causes the television sethorizontal retrace to occur early in each video line where either whenthe black or gray rectangle is present, depending on picture content andthe characteristics of the videotape recorder and TV set. The blackcheckers and gray checkers each may cause a transition of sufficientamplitude depending on the previous active video picture content. If thepicture content is light (white), the left edge of the black checkercauses a negative-going transition to black; if the picture content isdark, the right edge of the gray checker causes a negative-goingtransition from gray to the following dark area (typically blankinglevel). The difference between lines ending in black or gray in turncauses a horizontal displacement to the picture information, i.e. awiggle, which moves slowly up or down the picture.

The tendency of a television set to retrace (perform the horizontalflyback early) is exploited by providing the light to dark transition(the left edge of the black checker or the right edge of the graychecker) prior to the location in the video line of the genuinehorizontal line synchronization (sync) signal. The early retrace sotriggered causes the picture information on the succeeding line to beadvanced, i.e. displaced horizontally to the right by an amount equal tothe distance between the negative transition and the location of theleading edge of the genuine horizontal sync signal. This displacementcauses a "tearing" (horizontal repositioning) of picture information.

A somewhat similar modification in the vertical picture sense insertsalternating dark and white bands in place of active video in the lastfew lines of selected video fields in the lower overscan portion of thepicture just prior to the vertical blanking interval, and/or extendinginto the first few lines of the vertical blanking interval.

This vertical rate modification is implemented in several ways. In oneembodiment several of the active video lines (five or so) immediatelyprior to the vertical sync signal are made to alternate between blankinglevel and a gray level (typically about 30% of peak white) at a rate ofabout 1 to 5 cycles per second. This can cause drum servo unlock in thecopying videotape recorder, or erroneous vertical retrace in the TV set,causing the picture from the unauthorized copy to exhibit verticalinstability (jump up and down) at that particular rate, substantiallydegrading the quality of the image. In another version, two to fivelines of alternating (modulated) white-black-white are inserted at theend of each or alternate video fields, with the same result of loss ofvertical lock in a copying videotape recorder or viewing TV set due tointerpretation of the inserted pattern as a vertical sync signal whenthe video signal amplitude has been reduced through AGC response to acopy protection signal.

These vertical modifications in another version are both extended intothe first few lines of the subsequent vertical blanking interval.

Addition of pulses to portions of the video signal after normalhorizontal or video synchronization pulses cause an abnormal videoretrace at this point, thereby being an effective enhancement to theprior art basic anticopy process. Typically these added post-verticalsynchronization pulses are at e.g. lines 22-24 of an NTSC televisionsignal.

Thus, the processes in accordance with the invention ensure optimumconditions in terms of picture content for causing the maximum level ofsubjective degradation (1) to the replayed picture quality of theunauthorized copy and (2) to the recording and playback functions ofvideotape recorders.

The television set in response to the horizontal and verticalmodifications erroneously performs the horizontal or vertical retrace atan abnormal point. In the same way that a TV set will misinterpret thesignal, both the recording videotape recorder when the copy is made orthe playback videotape recorder when the copy is replayed can also beaffected. In this case it is the color circuitry of the videotaperecorder which is affected, with resultant picture degradationadditional to that caused by the basic anticopy process. This is anadditional effect to what has been described so far. This is because ofthe special way a videotape recorder processes the color information.The picture distortions include inaccurate color rendition andintermittent or permanent loss of color. The objective of themodifications thus is to further destroy the entertainment value of theillegal copy, over and above the degradation of the picture qualitycaused by the above-described basic prior art copy protection process.

The third modification to the video signal involves narrowing horizontalsync pulses. In combination with a copy protected video signal havingreduced signal amplitude when re-recorded (copied), this narrowingcauses the sensing of spurious vertical sync signals by a videotaperecorder or TV set, causing vertical retrace to take place at other thanthe beginning of a field and so further degrading picture quality. Thismodification narrows the width (duration) of the horizontal sync pulseson certain lines (such as lines 250-262) of the video field. Thesenarrowed horizontal sync pulses, when combined with a video signal thatis of diminished amplitude, trigger a spurious vertical retrace in manyTV sets and videotape recorders, further degrading the displayedpicture. Narrowing the horizontal sync pulses where the checker patternsexist (lines 10-250) also enhances the checker pattern distortion whenan illegal copy is made.

It has been observed that the degradation of the picture quality inaccordance with the present invention is particularly useful where theprior art basic copy protection process provides relatively smalldegradation of picture quality or relatively small degradation ofvideotape recorder recording or playback. Thus the combination of theprior art process and the present processes severely reducesentertainment value of the illegal copy on a much larger combination ofvideotape recorders and TV receivers than does the basic prior artprocess by itself.

Provision of the horizontal checker pattern or vertical modificationonly in the overscan portions of the television picture ensures thatwhen the original recording or signal is viewed there is no visibilityof the checker pattern or vertical modification, and indeed the presencethereof is not known to the viewer of the original recording.

In other embodiments, the process user might trade off picture area foreffectiveness. (The user may elect to trade off visibility of theprocess when the "legal" recording is played, in order to enhance theprocess anticopy effectiveness.) Thus, the modifications may inviolation of broadcast TV standards extend into the viewable portion ofthe video field, but still be acceptable in many applications.Furthermore, in another embodiment, the process trades off deviationsfrom accepted signal standards to further enhance the anticopyeffectiveness.

The modified signal in any case is displayed normally on any TV receiveror monitor, providing the signal is of the correct amplitude. When themodified signal amplitude is reduced, as on an illegal copy, theconditions are optimized for the TV receiver to display or for avideotape recorder to playback a distorted picture. This will occur in aback-to-back video tape recorder copying situation using two videotaperecorders when the recording being (illegally) copied is provided withthe basic anticopy process of the above-referenced U.S. Pat. No.4,631,603.

The video signal modifications in accordance with the invention, inaddition to causing lack of horizontal or vertical stability in a TVreceiver, also additionally have similar effects as described above on atypical videocassette (videotape) recorder, both during recording andplayback. VCRs use the leading edge of the horizontal sync pulse tocorrectly position the burst gate. If the burst gate is incorrectlypositioned, the color burst is not be sampled properly and loss of coloror distorted color results. The horizontal modification causesmisinterpretation of the position of the leading edge of horizontalsync. This will occur in the VCRs involved in both the recording andplayback of a (copy protected) copy, resulting in color loss/distortion.This effect can also be caused independently in the TV set. In the sameway that a TV set will tend to lose vertical lock as a result of thisprocess, so will a VCR. The result is a loss of drum servo lock in theVCR.

The modifications disclosed herein ensure that the required conditionsfor maximum picture disruption are always present, rather than relyingon chance (the particular picture being displayed) that these conditionsoccur. Therefore the above processes which may include the horizontaland/or vertical modifications and/or horizontal sync pulse narrowinghave substantial value in enhancing the above-described basic prior artcopy protection process, and more generally enhance any copy protectionprocess which reduces the amplitude of the video signal which isrecorded when an unauthorized copy is attempted. Another embodiment toenhance horizontal jitter with illegal copying of video tapes is to usepost horizontal pseudo sync pulses of approximately -20 IRE amplitude(-40 IRE equals normal sync amplitude) and a width of about 1-2 μsvarying in position in about a range of 1-2 μs after color burst.

While the embodiments disclosed herein are in the context of the NTSCtelevision standard, with modifications apparent to one of ordinaryskill in the art they are applicable to SECAM or PAL televisionstandard.

Also disclosed herein in accordance with the invention are severalmethods and apparatuses for removal or "defeat" of the above-describedvideo signal modifications, to permit unhampered copying and viewingthereof. The defeat method and apparatus in one version replace or levelshift the vertical and horizontal modification pulses with a fixed levelgray signal, and defeat the sync pulse narrowing modification by syncwidening or replacement.

In other versions, the defeat method uses added pre-horizontal syncpulses, post-horizontal sync pulses, or attenuation averaging. Alsodisclosed is a new method of defeating the prior art basic videoanticopying process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b show respectively a normal picture and a modifiedpicture with the horizontal modification checker pattern and thelocation of the vertical modification;

FIGS. 2a and 2b show a picture resulting from a video signal of normalamplitude, respectively without and with the checker pattern;

FIGS. 3a, 3b and 3c show the same pictures as displayed respectively ona television set with a video signal of reduced amplitude, without andwith the checker pattern and vertical modification;

FIG. 4 shows a portion of a video signal with the checker pattern;

FIGS. 5a and 5b show respectively a portion of a video signal with thevertical modification not extending into the horizontal and verticalblanking interval and with the vertical modification extending into thevertical blanking interval;

FIG. 5c shows an additional vertical modification extending into thehorizontal blanking interval;

FIGS. 6a, 6b, 6c show a circuit for providing video signal modificationsin accordance with the invention;

FIGS. 7a, 7b show waveforms illustrating operation of the circuit ofFIGS. 6a, 6b, 6c;

FIG. 8 shows detail of flicker generator of FIG. 6b;

FIG. 9 shows another embodiment of a circuit for providing the videosignal modifications;

FIG. 10 shows a prior art sync separator circuit;

FIGS. 11a to 11o show video waveforms illustrating horizontal sync pulsenarrowing;

FIG. 12a shows a block diagram of a circuit for horizontal sync pulsenarrowing;

FIG. 12b shows waveforms illustrating operation of the circuit of FIG.12a;

FIGS. 13a, 13b show in detail a circuit for horizontal sync pulsenarrowing;

FIGS. 14a, 14b, show block diagrams of apparatuses for combining syncpulse narrowing with the horizontal and vertical modifications;

FIG. 15 shows in block diagram form an apparatus for removal of thevarious video signal modifications;

FIGS. 16, 17, 18 show a circuit for removing the anticopy processenhancement signals via level shifting and horizontal sync replacement;

FIG. 19 shows a second circuit for removing the anticopy processenhancement signals via new sync and burst position replacement;

FIG. 20 shows a third circuit for removing the anticopy processenhancement signals via multiplying; and

FIGS. 21, 22, 23 show three additional circuits for removing theanticopy process enhancement signals via switching means;

FIGS. 24a, 24b, 24c show a circuit for nullifying the enhancementsignals using sync widening;

FIGS. 25a to 25h shows waveforms of the circuit of FIGS. 24a, 24b;

FIG. 26 shows another circuit for defeating the enhancement signals viaDC averaging and attenuation;

FIG. 27 shows an additional circuit of defeating the enhancement signalsvia clipping;

FIG. 28 shows yet another circuit to defeat the enhancement signals;

FIGS. 29a, 29b show waveforms illustrating defeat of the enhancementsignals via increasing sync amplitude;

FIG. 30 shows a circuit for defeat of the enhancement signals viaincreasing sync amplitude;

FIG. 31 shows another circuit for defeat of the enhancement signals viatracking and holding circuits;

FIGS. 32a, 32b show waveforms illustrating defeat of the enhancementsignals via adding an AC signal;

FIG. 33 shows a circuit for connecting circuits for defeat of theenhancement signals;

FIGS. 34a, 34b and 34c show waveforms illustrating sync slicing;

FIGS. 35a, 35b show waveforms illustrating the effect of widened sync;

FIGS. 36a, 36b show further sync slicing points;

FIG. 37 shows a circuit for enhancements of a checker pattern usingpost-sync pulses;

FIGS. 38a to 38e show waveforms illustrating operation of the circuit ofFIG. 37;

FIG. 39a shows a circuit for defeat of the post-sync pulses enhancement;

FIGS. 39b to 39d show waveforms illustrating operation of the circuit ofFIG. 39a;

FIGS. 40a, 49d, 40g show circuits for defeat of post-pseudo sync pulses;

FIGS. 40b, 40c, 40e, 40f, and 40g show waveforms illustrating operationof the circuits of FIGS. 40a, 40d, 40g;

FIG. 41a shows a circuit for defeat of post-pseudo sync pulses by pulsenarrowing;

FIG. 41b shows a corresponding waveform illustrating operation of thecircuit of FIG. 41a;

FIGS. 42a, 42b show a circuit for defeat of the prior art basicanti-copy process;

FIGS. 43a to 43g show waveforms illustrating operation of the circuit ofFIGS. 42a, 42b.

DETAILED DESCRIPTION OF THE INVENTION

Horizontal Rate (Checker) Signal Modification

FIG. 1a shows a normal television picture 10, (without showing anyactual video information), i.e. including the left and right overscanportions 14, 16 and top and bottom overscan positions 7, 9. The part ofthe picture inside the dotted line 13 is the visible video 11.

The overscan portion of a television picture, as is well known, is thatportion of the television picture not viewable on a standard televisionset. Because of design limitations and aesthetic considerations,standard TV sets are adjusted by the manufacturer to display somewhatless than 100% of the transmitted picture area. The portions of thetelevision image which are not normally viewable are called the overscanarea. These portions are viewable on a professional-type video monitorwith underscan capability. However, all standard television receiversoperate in an overscan mode, and hence the added checker pattern and themodified lines at the end of each field would not be viewable on suchstandard television receivers as sold in the United States andelsewhere.

FIG. 1b shows the modified television picture 12 in accordance with thecertain modifications of the present invention, also including theoverscan portions 14, 16. In the right-side overscan portion 16, achecker pattern 20 of alternating gray rectangles 24 and blackrectangles 26 is provided. This checker pattern information 24, 26provides the copy protection enhancement as described below. In thedisplay of the picture 12 on a standard TV set the checker pattern 20would not be seen since it is in overscan area 16. The vertical signalmodification is inserted in the bottom overscan area 9 and therefore isalso not visible.

FIG. 2a shows a video field 30, including the left and right overscanportions 32, 34, including in the active video 36 a vertical andhorizontal picture element 38 (such as for instance a cross). This field30 is in accordance with the prior art and the checker pattern andvertical modification signal are clearly not included. This is alsowithout any reduction of signal amplitude, i.e. without provision of theprior art copy protection process.

FIG. 2b shows the field 30 with the addition of the checker pattern 42in overscan area 34 outside border 13 and the addition of verticalmodification pattern 87 to lower overscan portion 9. Since there isnormal signal amplitude present, the checker pattern 42 and/or verticalpattern 87 have no effect on the appearance of the cross 38 which isshown normally. It is to be understood that FIG. 2b is what would appearon a monitor showing the entire area and would not appear on a normaltelevision receiver.

It is not possible to show a graphic representation of the effect ofthese signals on the VCR. A TV set will display artifacts due to theabnormally low signal amplitude; the VCRs used to record and replay thecopy can also be affected. In this instance, the servo systems of theVCRs will be disturbed, resulting in positionally unstable pictures.

FIG. 3a shows a picture 50 resulting from reduced signal amplitude, i.e.in accordance with the prior art copy protection process, acting on arelatively insensitive VCR, but without the addition of the checkerpattern. This figure shows only the actual viewable portion (insideborder 13 of FIGS. 2a, 2b) of the picture on a standard televisionreceiver. As can be seen, the cross 38 is displayed normally because inthis case the picture content is such that there is no horizontaldisplacement. This is a case where the prior art copy protection processprovides inadequate copy protection, because the picture is indeedviewable.

FIG. 3b shows the effect of the presence of the checker pattern 42 ofFIG. 2b when the reduced signal amplitude is present, i.e. when theprior art copy protection process is used in conjunction with thechecker pattern. Again in FIG. 3b the overscan portion is not shown.Here it can be seen that the cross 38 suffers from multiple horizontal"tears" 43 which occur at the location of the transition from graychecker 46 to black checker 44 (and vice versa) of the checker pattern42 of FIG. 2b. As shown in the enlarged view of FIG. 3c, portions 43 ofthe vertical part of cross 38 are horizontally displaced by an amountdependent on the distance between the left edge of the black portions 44of the checker pattern and the location of the true horizontal syncsignal in each line (not shown). Clearly, the picture 50 of FIG. 3b issubstantially degraded. The effect is further enhanced (not shown) bymoving the checker pattern 42 up or down slowly in the verticaldirection so that the horizontal displacements are seen to move, i.e."wiggle". This provides a virtually unviewable picture and hencesubstantial copy protection.

In accordance with the invention the checker pattern 42 of FIG. 2bincludes typically five black rectangles 44 each alternating with one ofthe mid-gray rectangles 46. (Fewer such rectangles are shown in FIG. 2bfor clarity). It has been found that maximum picture degradation occurswith approximately five gray to black transitions and five black to graytransitions per picture height.

The signal level of the black rectangles 44 is set to be betweenblanking level and black level for NTSC (black level and blanking levelare the same for PAL or SECAM signals), and at black level for PAL andSECAM, and the amplitude of the mid-gray rectangles 46 is approximately30% of peak white level. The checker pattern 42 induces the zig-zag typepattern as shown in FIG. 3b; in other embodiments, there might be onlyone black rectangle 44 or two, three or four or more black rectangles 44per field 30 of FIG. 2b. Also the sizes (heights and widths) of theblack rectangles 44 need not be uniform.

The process causes early horizontal retrace in a low video signalamplitude environment by providing a negative-going transition, i.e.from the instantaneous picture level at the start point of the blackrectangles 44 to black level prior to the horizontal sync signals on atleast certain lines of the picture. The checker pattern 42 shown in FIG.2b is one such pattern which causes the intended effect.

The typical duration, (width) of the checker pattern 42 is approximately1.0 to 2.5 microseconds, as determined by the requirement that thechecker pattern normally is not introduced into the displayed portion ofa standard television picture, i.e. is limited to the overscan portion,and also does not infringe upon the normal horizontal blanking period.

In other embodiments, the horizontal sync pulse is narrowed and allowingthe checker pattern to be wider. This would provide a greater horizontaldisplacement when the reduced amplitude video signal is displayed, butresult in a nonstandard original video signal, which however isacceptable for certain non-broadcast applications. Also, the particularamplitudes of the mid-gray 46 and/or black rectangles 44 need not beexactly as described above. Any effects resulting from the changedrelative position of leading edge of horizontal sync pulse and the colorburst can be corrected by a corresponding relocation and/or expansion ofthe color burst.

FIG. 4 shows the horizontal blanking interval 60 for a single videoline, with a portion of the checker pattern present. The horizontal syncpulse 62 conventionally starts 1.5 microseconds after the start of thehorizontal blanking interval 60. Active video 66, 68 occurs both beforeand after the horizontal blanking interval 60. However, in accordancewith the invention, a portion 70 of the active video 66 just prior tothe horizontal blanking interval 60 has been replaced by either amid-gray level signal 74 or by a black level signal 76. (The gray level74 and the black level 76 are both shown in FIG. 4 only for purposes ofillustration.) The loss of portion 70 of the active video 66 is notproblematic, since as explained above in a standard television receiverthis portion of active video is not visible anyway, being in theoverscan portion of the picture.

The transition 80 from the active video level 66 down to the black level76 appears to the television receiver to be a horizontal sync signal.This effect (as explained above) only occurs when the video signal beingdisplayed has reduced amplitude due to the copy protection process.

The presence of the gray level 74 (the gray portions of the checker)additionally ensures that the entire picture is not shifted to theright. This would be the case if for instance there was a solid blackstripe down the right hand side of the picture. The alternating gray andblack levels provide the zig zag effect shown in FIG. 3b, which has beenfound to be intolerable for viewing by virtually any individual. Alsoshown in FIG. 4 is a conventional color burst 82 riding on the backporch 84 of the horizontal blanking interval 60.

It will be appreciated from FIG. 4 that the only modification to thevideo signal is the removal of the small portion of active video 70 andthe substitution therefore of either the gray level 74 or black level76.

The above described wiggle enhancement causes the checker pattern tomove slowly from the bottom to the top of the picture or vice versa. Itis found that if this takes approximately one second for a giventransition to migrate from the bottom of the picture to the top of thepicture or vice versa, this causes optimum reduction of entertainmentvalue of the picture. This moving wiggle effect is provided by using afrequency of the square wave that generates the checker pattern beingslightly offset from the fifth harmonic of field rate, i.e. between 295Hz and 305 Hz, for NTSC television. The corresponding frequency for PALor SECAM systems is 245 to 255 Hz. This nonsynchronicity provides thedesired slow movement of in the checker pattern. As noted above, even ifsuch asynchronicity is not present and the checker pattern is static,there is still substantial benefit from the present process. Thefrequency of the signal generating the checker pattern can be adjustedto maximize the degradation of the picture quality when the lowamplitude signal is replayed and displayed. Frequencies between 180 and360 Hz for NTSC and 150 to 300 Hz for PAL (3 to 5 times the field rate)typically result in an optimum effect. The frequency may be varied withtime to ensure optimum effect on a variety of playback and viewingequipment.

In another embodiment, the checker pattern is located on the front porchof the horizontal blanking interval, i.e. not replacing any portion ofactive video. This somewhat reduces the amount of horizontaldisplacement; however, still there is at least some of the desiredeffect but resulting in a signal which retains all of the pictureinformation but does not conform to all NTSC standards.

The checker pattern need not be present on every field.

Vertical Rate Signal Modification

The above detailed description is directed to horizontal pictureinformation; the video signal modification and the consequent effect ofthis modification are in the horizontal picture direction. The relatedvertical rate modification described in the Summary is further describedhereinafter.

The vertical modification takes several forms. In one embodiment, groupsof 1 to 4 lines in the lower overscan portion of a video field havetheir active video replaced alternatively with white or black. Inanother embodiment, the last few video lines immediately prior to thevertical sync pulse are blanked, as are the first few lines of thefollowing vertical blanking interval, and the original picture video andvertical sync pulse therein are replaced with either a high level (suchas mid gray which is about 30% peak white, or actual peak white) or alow level (in the range of black down to blanking level) signal as shownat 87 in FIGS. 1b, 2b and described above.

These vertical modifications are normally not visible to the viewersince the modified active video lines are restricted to those linesfalling in the overscan area 9 at the bottom of the picture of FIG. 1b.(Also, the modified lines will be in a similar location to the headswitch point when video from a VCR is considered, and video on theselines is unusable in any case as a result of disturbances occurring atand after the head switch point.)

In a standard NTSC video signal (or in other standards) as is wellknown, the first three lines of the vertical blanking interval eachinclude two equalization pulses, and the following three lines eachinclude two "broad" vertical sync pulses. Normally vertical retracebegins shortly after the first of these vertical sync pulses.

The first vertical modification embodiment is shown in FIG. 5a. (Linenumbers here refer to the second field of an NTSC video frame.) Lines517, 518, 519 have their active video portions replaced with a peakwhite (1.0 volt nominal) signal; the same is done in lines 523, 524,525. In lines 520, 521, 522 the active video is replaced with a black (0volt nominal) signal. Instead of groups of three lines, the groups maybe 0 to 5 or more lines, and the white and black signals may bemodulated or switched in amplitude. Thus in the last several lines ofeach field the pattern of the white and black signals changesdynamically between fields.

The second vertical modification embodiment (FIG. 5b) blanks the lasttwo active video lines (lines 524 and 525 for instance) in a video fieldand the first three lines (lines 1, 2, 3 for instance) of theimmediately following VBI. These two active lines are in the loweroverscan portion 9 (FIG. 16) of the TV picture. Then a mid gray (30% ofpeak white) video signal 87 is generated and inserted in these fiveblanked lines on a periodic basis. When the mid gray signal is not on(indicated by vertical arrows at lines 524, . . . , 3), these blankedlines "fool" the vertical sync circuitry of most TV receivers intoperforming the vertical retrace at the beginning of the first of thesefive lines, rather then normally five lines later at the beginning ofthe vertical sync pulses. Thus vertical retrace is advanced by fivelines. When these five lines are at mid gray, vertical retrace isinitiated at its proper location by normal vertical sync. It is to beunderstood that the number of such blanked lines and the amplitude ofthe inserted waveform may vary in other embodiments.

As shown in FIG. 5b, lines 4-6 (only 1-4 are shown) are as in a standardsignal, as are lines 517 to 523. The modification is only to lines 524,525, 1, 2 and 3; the active video portions of lines 524, 525 and thecorresponding portions of lines 1-3 are blanked (to black) or have a midgray signal at about 0.3 volts inserted. (It is to be understood thatthis amplitude is nominal, without consideration of the amplitudereduction effect of the associated prior art copy protection process).FIG. 5b shows a portion of a field with the mid-gray level. As statedabove, the gray signal is switched on and off ("oscillates") at a ratetypically between 1 Hz and 10 Hz. In the version oscillating at 1 Hz,there are 30 consecutive video fields with five lines having activevideo at blanking level, followed by 30 consecutive video fields withthe five lines at 30% gray of FIG. 5b. As shown in FIG. 5b, the colorburst in lines 524 to 3 may be blanked (or not).

This oscillation causes the picture to "jump" up and down by 5 linesonce per second (the oscillation rate) which has been found to beextremely irritating to the viewer as suggested at "x" in FIG. 3b. Thatis to say, on the fields where the vertical modification of FIG. 5b ispresent, the vertical retrace occurs early by five lines, followed bythe fields where the vertical retrace occurs normally. The earlyvertical retrace occurs because the overall video amplitude has beenreduced for instance to a maximum (peak white to sync tip) of 0.4 voltsfrom the NTSC standard 1.0 volts due to the presence of the prior artcopy protection signals. The vertical sync separator of the TV receiverthen perceives the first of the five blanked lines as being the firstvertical sync (broad) pulse and so retraces vertically shortlythereafter.

In another version of the vertical modification (not shown) instead ofthe last two lines of one field and the first three lines of the nextfield being modified as in FIG. 5b, the modification is wholly to thelast five lines (lines 521, 522, 523, 524, 525) of active video of onefield; this avoids producing an "illegal" (non-standard) video signal. Avariation of this vertical modification is to relocate about 3 lines ormore like lines 524, 525, and in FIG. 5b to lines after the verticalsync area (i.e., lines 22-24). In some TV sets this causes extra jumpingbecause the TV set "sees" two vertical sync pulses one at the right timei.e., line 4 and one at about line 23.

It is to be understood that the vertical modification need not extendover the entire active video portion of a horizontal line. It has beenfound that providing the modification over about 1/2 of the duration ofactive video in a line is sufficient to generate the premature verticalretrace.

In yet another embodiment of the vertical modification (similar in mostrespects to that of FIG. 5a) as shown in FIG. 5c, the horizontalblanking interval is removed (blanked) on lines 517, 518, 519, 523, 524,525 where the white pulses are added. Therefore (like that of FIG. 5b)this is also an "illegal" (non-standard) video signal, but is acceptablefor many non-broadcast applications. The elimination of horizontalblanking on these lines increases AGC gain reduction (in VCR AGCcircuits). The white pulses on lines 517, 518, 519 and 523, 524, 525 maybe present in each field or modulated or switched in amplitude.Moreover, these lines with white pulses may change locations by a fewlines from field to field or some multiple of field rate as to inducevertical blurring effects when an illegal copy is made and viewed on aTV set. The groups of white pulses may extend over zero to four lines.

The vertical modifications to the video signal have no effect whenapplied to a TV monitor as a part of an original (authorized) signal.However, if the video signal amplitude is reduced sufficiently, forexample by an anticopy process, the TV monitor will tend to incorrectlydetect the vertical sync information, with vertical instabilityresulting as described above.

Furthermore, if the vertically modified signal is applied to a VCR inconjunction with an anticopy process which results in a reducedamplitude video signal within the recording VCR, when a recording ismade the VCR's drum servo will tend to be disturbed. This is becauseVCR's typically require a "clean" vertical sync signal to maintaincorrect phase, and the presence of a jittering vertical sync signalcauses the VCR to lose lock. When the recording is replayed the visibleeffect is vertical instability of the picture plus intermittent noisebands which appear as the drum servo loses lock. (This is similar to avariable tracking error.)

In other words, the vertical rate waveform modifications functionsimilarly to the horizontal rate waveform modification described above,except that vertical disturbances are induced rather than horizontal.The two techniques combined are more effective in terms of picturequality degradation than either one on its own. Sweeping the pulse rateof the vertical waveforms increases effectiveness to more TV sets, i.e.,the frequency is varied between for instance 2 Hz and 10 Hz over aperiod of about 20 seconds. Sweeping the checker frequencies also willcause the horizontal tearing to go up and down resulting in a moreirritating picture when an illegal copy is made.

Apparatus For Vertical And Horizontal Modifications

Circuitry for inserting the above-described horizontal and verticalmodifications is shown in block form in FIG. 6a.

The main video signal path includes an input clamp amplifier A1; a syncpulse narrowing circuit 96; a mixing point 98 at which the waveformcomponents of the horizontal checker and the vertical modification(jitter inducing) waveforms are added; and an output line driveramplifier A2. In this case also the video input signal into the circuitof FIG. 6a may have the last 9 lines of each field blanked to areference level. U.S. Pat. No. 4,695,901 shows a switching circuit forblanking.

The process control and signal generation path includes a sync separator100; control circuit 102; circuits (see FIG. 6b) to generate therequired signal voltages which will be added to the main video signal;and a switch selection system 104 (FIG. 6a) which applies the requiredsignal voltages under the control of the control circuit 102. (Note thatin the drawings certain parts designations, e.g. U1, R1, OS1, A1 are onoccasion repeated for certain components. These are not intended torepresent the identical component unless explicitly indicated.)

The input video is DC restored by the input video clamp amplifier A1.(Amplifier A1 is a commercially available part, for example the ElantecEL2090.) Amplifier A1 ensures that the video signal (at blanking) is ata known pre-determined DC level before adding any additional waveformcomponents to that video signal.

The resulting clamped video signal is applied to the mixing point 98with a source impedance Ro, typically greater than 1000 ohms. The addedpulse signals to be injected are applied to the mixing point 98 with asource impedance less than 50 ohms. When it is required to modify theinput video signal, for example with a checker component, theappropriate signal is selected and applied to the mixing point at a lowsource impedance, which overrides the input video signal from amplifierA1 and effectively replaces the input video signal with the requiredsignal. When the input signal is to remain unchanged, the switchelements 104 are all in the open state, with the result that the videosignal passes unchanged to the output line driver amplifier A2. Theresulting video signal at the mixing point 98 is applied to line driveramplifier A2 to provide standard output signal level and outputimpedance. An output of the video clamp amplifier A1 is applied to thesync separator 100 (this is a commonly available part, for example theNational Semiconductor LM 1881.) Sync separator 100 provides thecomposite sync pulses and frame identification signal required by theprocess control circuit 102.

The process control circuit 102 generate the control signals to turn onthe signal selection switches 104 at the precise time (and for therequired duration) that the various signals are to replace the inputvideo signal.

All of the various signals which are to replace the original (input)video consist of a high or low steady state DC signal level. For examplethe checker signal "high" is a mid-gray level, typically of about 30% ofpeak white; the checker signal "low" is black level or blanking level.These various signal levels are generated (see FIG. 6b) frompotentiometers VR₁, VR₂, VR₃, VR₄ which provide adjustable signal levels(or alternatively from voltage divider resistors for fixed preset signallevels) connected across appropriate supply voltage lines. This signalis applied to the appropriate selection switch elements respectively104-1, 104-2, 104-3, 104-4 via unity gain operational amplifiers A5 toensure the required low output impedance into the mixing point 98.

The control circuit 102 generates the appropriate switch selectioncontrol pulses for the checker pattern and vertical modification signals(see FIG. 6a). Checker pulses are applied only to selected lines; oneexample is to start the checker pattern at the 10th line containingpicture information (i.e. after the end of vertical blanking) and end it10 lines before the last line containing picture information (i.e. 10lines before the start of the succeeding vertical blanking interval).Similarly, the vertical jitter modification signals are be applied onlyto selected lines, for example the last nine lines prior to the verticalblanking interval. Hence, both the checker pattern and verticalmodification signals require control signals with both horizontal andvertical rate components.

The video input signal "video in" (see FIG. 6c showing detail of FIG.6a) is buffered by amplifier A3 and coupled to sync separator viacoupling capacitor C1 and a low-pass filter including resistor R1 andcapacitor C2. Sync separator 100 provides composite sync pulses andframe identification square wave signals. The composite sync pulses areapplied to a phase-locked loop (PLL) 110. The phase control ("phaseadj.") of PLL 110 using potentiometer VR₆ is adjusted so that thehorizontal rate output pulse starts at the required start point of thechecker, typically 2 μs before the start of horizontal blanking (FIG.7a). The output signal of PLL 110 is used to derive the horizontal ratecomponent f_(H) of both the checker and vertical modification signals.The burst gate output signal of sync separator 100 is inverted byinverter U5 which provides a clamping pulse for clamp amplifier A1 (partnumber EL2090).

The frame identification square wave output ("frame pulse") of syncseparator 100 is applied to a one-shot circuit OS1 to provide a frameidentification pulse of approximately 1 μs duration. This one-shotoutput signal f_(v) is used to derive the vertical rate component ofboth the checker and vertical modification signals. The horizontal-ratephase-locked loop component f_(H) from PLL 110 is applied to the clockinput terminal of a memory-address counter 114. The frame(vertical)-rate one-shot output signal f_(v) is applied to the resetinput terminal RS of counter 114. The memory address counter 114 outputsignals are applied to the memory 116, typically an EPROM which isprogrammed such that one of its data line output terminals provides achecker pulse enable (CPE) signal which is high during that portion ofthe picture period that the checker signal is to be present. A secondEPROM data line output terminal provides an end-of-field identification(EFI) signal which is high during the lines at the end of each fieldwhich will have to include vertical modification signals.

The horizontal-rate phase-locked loop component f_(H) is also applied toa one-shot circuit OS2 which generates an end-of-line pulse (ELP) of therequired duration of the checker pulses, typically 2 μs (see FIG. 7a).

The horizontal-rate phase-locked loop output signal f_(H) is alsoapplied to another one-shot circuit OS3, providing an output pulse ofapproximately 13 μs duration. The output of one-shot OS3 triggersanother one-shot OS4 with an output pulse VJP of approximately 52 μsduration. The timing and duration of pulse VJP define the position ofthe vertical modification inducing signal within the line time; i.e.pulse VJP is essentially on during the desired portion of the activehorizontal line period.

The four signals ELP, VJP, CPE and EFI generate the required controlsignals for the signal selection switches 104-1, . . . , 104-4 (see FIG.6b). The end of line pulse ELP is applied to a divider circuit 122 toderive the desired frequency to determine the checker frequency. Thehigher this frequency, the greater the number of checker dark-light-darktransitions per picture height. This frequency may be chosen within awide range; a divider ratio of 52 (n=52) provides a useful result. Thedivider 122 output signal is applied directly to one input terminal of3-input AND gate U4. An inverted output signal of divider 122 is appliedto the corresponding input terminal of second 3-input AND gate U5. Theoutput portino of divider 122 can be a sweep oscillator circuitconsisting of a pair of NE566 IC's. One NE566 is set nominally at 300 Hzand the other is set at 1 Hz. The output of the 1 Hz NE566 is fed to thefrequency control input of the 300 Hz NE566. Both 3-input AND gates U4,U5 have the checker pulse enable (CPE) and end of line pulse (ELP)signals applied to their two other input terminals. The result is a highchecker control (HVJ) signal at the output terminal of 3-input AND gateU4, and a low checker control (LVJ) signal at the output of 3-input ANDgate U5.

A similar arrangement generates the required signals for the verticalmodification control signals. An oscillator 126 (such as thecommercially available part number NE555 or NE566) is configured tooperate at low frequencies, typically between DC and 10 Hz. Theoscillator 126 can be set to a high logic level output. Similarly the DCto 10 Hz signal output can be swept over a range of frequencies to upsetas many TV sets as possible during playback of an illegal copy. This canbe done as described above with a pair of NE566 IC's. The output signalof oscillator 126 is applied to one input of a 3-input AND gate U2. Aninverted output signal of oscillator 126 is applied to the correspondinginput terminal of a second 3-input AND gate U3. Also, each TV set may"resonate," or jitter more at unique frequencies sweeping thefrequencies of oscillator 126 ensures wide coverage of different TVsets. The vertical jitter position (VJP) and end of field identification(EFI) signals (with signal EFI modified by flicker generator 130 and sodesignated EFI') are applied to the other two input terminals of 3-inputAND gates U2, U3. The result is a high vertical jitter control (EFC H)signal at the output terminal of 3-input AND gate U2, and a low verticaljitter control (EFCL) signal at the output of 3-input AND gate U3.

It will be understood that with suitable modifications, the aboveapparatus will produce the added horizontal or vertical modificationsafter the normal horizontal or vertical sync signals, e.g. for the addedvertical modifications at lines 22-24 of an NTSC television signal, soas to cause a video retrace.

The circuit of FIG. 6b in conjunction with flicker generator circuit 130via EFI' produces multiple vertical modification signal patterns.

FIG. 6b shows the field or frame "flicker feature" generator 130 used incertain embodiments of the invention for modifying the horizontal andvertical modifications.

The following are achieved by this flicker feature:

1) Change the "polarity", i.e., invert the gray vs. black rectangles ofthe checker pattern at some particular multiple of field rate; this willfor instance cause the attenuated video from an unauthorized copy tointerleave the checker displacement, further degrading the viewabilityof the copy.

2) A field-by-field change of the position of the end of field (verticalmodification) pulses causes the authorized copy to playback on a TV setan up/down flicked blur, because each field has a differently timedpseudo-critical sync pulse position. This is achieved for example if:

EFI pulse is high on lines 255-257, and

EFI1 pulse is high on lines 258-260, and

EFI2 pulse is high on lines 261-262 and 1, and

EFI3 pulse is high on lines 21-23.

FIG. 8 shows the circuitry of flicker generator 130 of FIG. 6b, andshows that these four pulses are multiplexed via multiplexer U10 (i.e.,a CD4052) at a field rate by EPROM U8 (part number 27C16 or 2716). As aresult, pseudo-vertical sync pulses occur differently in positiondepending on the field. In a simple example, EFI, EFI1, EFI2, EFI3 arestepped once per field. As a result, during playback of an unauthorizedcopy, the pseudo-vertical occur at lines 256 or 259 or 262 or 22 insuccessive fields or frames. As a result, the picture flickers becauseof the field rate vertical sync repositioning in the TV or VCR. EPROM U8provides flexibility as to where the various end of field pulses are tobe located as a function of time.

FIG. 8 also shows how the checker pattern black vs. gray rectangles areinverted at some particular multiple of field rate. The vertical syncpulses clock the 8 bit counter U7 (divide by 256, part number 74HC393).The outputs of counter U7 drive the address lines of the EPROM U8. Thedata output signal DO from EPROM U8 goes high to invert the checkerpattern via switches SW1K, SW2K. The flexibility of signal DO from EPROMU8 allows the invert commands on the checker pattern to happenpseudo-randomly or periodically, and also allows different flicker rates(i.e. every 2 fields or every 5 fields, etc.). EPROM U8 data lines D₁and D₂ also drive multiplexer switch U10 (part number CD4052), similarlyimproving flexibility to generate output signal EFI'.

Another Circuit For Generating The Vertical And Horizontal Modifications

In FIG. 6b the end of field and end of line pulses are switched throughto override the video driving resistor R₀. Unless these switches have alow enough "on" resistance, video from the input program source willalways superimpose on top of the end of field or end of line pulses. Forexample, a typical analog switch on-resistance is about 100 ohms. Thetypical resistance R₀ is about 1000 ohms. With these values, 10% of thevideo superimposes on the end of line and end of field pulses. If thevideo goes to peak white, the end of field and end of line pulses willhave a minimum of about 10% peak white (100 IRE) or 10 IRE thusrendering these added pulses useless.

To overcome these possible shortcomings, in another embodiment the addedpulses are added then switched in via multi-pole switches that at thesame time switch out the video source.

As shown in FIG. 9, the end of field high and low states are generatedby AND gate U23 with input from oscillator U22 (a 0.1 Hz to 10 Hzoscillator) and input signals VJP and EFI. Switch SW103 switches betweenthe high and low states controlled by variable resistors R_(B) and R_(A)respectively. Amplifiers A10A, A10B are unity gain buffer amplifiers. Toensure against crosstalk of low states of EOF and checker pulses, switchSW103A is connected between switch SW103 and amplifier A100, and switchSW102A is connected between switch SW102 and amplifier A101. Gate U23A"and" gates switch SW103A to go to ground on all lines other than theEOF line locations. Likewise, gate U21A gates switch SW102A to ground atall times other than when the checker pulses are on. Otherwise, switchesSW103A and SW102A are transparent to the EOF and checker pulses ofswitches SW103 and SW102, respectively. The output of switch SW103 isbuffered by unity gain buffer amplifier A100 and summed into a summingamplifier A102. Similarly, switch SW102 receives the end of line high,low states generated via signal ELP, counter U20 (a divide by ncounter), and signal CPE.

Variable resistors R_(c) and R_(D) provide adjustment for high and lowend of line pulses respectively. Amplifier A101 buffers switch SW102into slumming amplifier A102 via resistor R2. Amplifier A102 feedssumming amplifier A103. The post pseudo-sync pulse (PPS) is also summedinto summing amplifier A103. The output of slumming amplifier A103 isthen: end of line pulses, end of field pulses and post pseudo-sync pulse(PPS). Switch SW101 switches in all of these pulses via OR gate U10 andinverter U11 during their coincident times, and switches in video at allother times. Amplifier A104 buffers output of switch SW101 and provide avideo output "Video Out" containing video with the added pulses. SwitchSW104A preblanks to video from the sync narrowing circuit to a voltagelevel VBLNK (i.e. 0 IRE) for the last active 9 lines of each TV fieldvia "AND" gate U104B. Gate U104B has EPROM data output EFO (which turnshigh during the last 9 lines of the TV field) and VJP (active horizontalline pulse) at its two inputs.

A position modulation source for the PPS is controlled by voltage sourceVgen. Source Vgen feeds resistor R20 with an inverted burst gate pulseinto resistor R10 and capacitor C2 to form a variable delay into oneshot U20. One shot U20 is approximately 1.5 μsec of variable positionafter burst of input video, and is gated out during the verticalblanking interval by signal CPE and NAND gate U21B. Resistor R6determines the amplitude of the PPS. Resistor R6 is typically set to -10RE to -20 IRE. The other input (U22A) of "NAND" gate U21 is normallyhigh as to all PPS to be a constant amplitude pulse position sync. IfU22A is pulsing (i.e., 300 Hz), the PPS signal is then turning on andoff as well (at 300 Hz). Thus, the PPS can be a position modulatedpulse, and pulse amplitude modulated sync pulse following burst.

Horizontal Sync Pulse Narrowing Modification

A sync pulse narrowing circuit and method for enhanced of an anticopyprotection of video signals is used by itself or in cascade (as shown inFIG. 6a block 596) with any of the above-described other signalmodification techniques, and as further described below. The reason tonarrow the video signal sync (synchronization) pulses (mainly thehorizontal sync pulses) is so that when an illegal copy is made, theattenuated video with reduced sync pulse width (duration) causes aplayability problem when viewed on a TV set. This is because most TV setsync separators incorporate sync tip DC restoration. Because these TVset sync separators are typically driven by medium impedances, the syncpulses are partly clipped off. By narrowing the sync pulses, the syncpulses are even further clipped off. When an unauthorized copy is madeof the video signal, especially with the above-described checker and/orend of field modification signal, the copy has a reduced amplitude videowith reduced sync pulse width. As a result, the TV sync separator sees asevere loss in sync due to its own clipping from the narrowed sync widthand the attenuation of the video itself. Thus, the TV set's syncseparator does not "extract" sync properly and this causes the TVpicture to be even less viewable, because the horizontal and/or verticalmodification effects are more intense.

FIG. 10 shows a typical prior art sync separator as used in many TVsets. This circuit operates when the inverted video is fed to the baseof the transistor Q1 via a coupling capacitor C. The sync tips of thevideo signal charge up the capacitor C, just enough so that only thevery tip of the sync pulses turn on the transistor. Resistor R_(b)biases the transistor so that the tips of sync are "sliced" The voltageVc across C, is related to resistance R_(o) the driving resistance ofthe video. The larger resistance R_(o), the more the amount of syncclipping is seen at V_(b). If resistance R_(o) is too large, thetransistor Q1 will start sync slicing into the video (blanking level)region, because the value of V_(c) is not charged up to an average levelto allow a cut off of the transistor just below the sync tip level ofinverted video.

Insufficient charging of capacitor C allows transistor Q1 to be turnedon even when blanking level arrives. The base emitter impedance oftransistor Q1 is low when transistor Q1 is on. (This causes attenuationof the positive going sync pulses). Since charging capacitor C is afunction of the sync pulses' width, narrowing the sync pulses makes thesync separator clip a portion of the narrowed sync more than a normalsync width. This is equivalent to sync slicing at a point closer to thevideo signal (i.e. video blanking level). Under normal video levels anarrowed sync pulse presents no playability problems on a VCR or TV. Butwhen a narrowed sync pulse is recorded on an illegal copy of a copyprotected cassette, the video signal is attenuated. This attenuationwith the narrowed sync causes the TV (during playback viewing) to notreliably extract the sync pulses and instead synchronize off parts ofthe video signal, i.e. blanking level.

Selectively narrowing certain horizontal sync pulses to close to zeropulsewidth (to less than 600 ns duration) so that the filter in a TV orVCR sync separator does not respond or that the sync separator couplingcapacitor charges up negligibly is equivalent to there being no syncpulse in that area. These selected horizontal sync narrowed pulses nearthe end of the field can create a situation such that the sync separatorwill slice a blanked video line as a new (spurious) vertical pulseduring playback. With a video signal from an illegal copy withattenuated video supplied to the TV, this situation then causes the VCRor TV to see two vertical pulses in one field, which can cause verticaljitter.

In one embodiment, the pulsation (modulation) frequencies of the end ofthe video field lines (those end of field lines having an amplitude 0IRE to at least 10 IRE having narrowed horizontal sync pulses) are sweptfrom about 1 Hz to 15 Hz. This advantageously causes the desired effectin a wide variety of TV sets.

FIG. 11a shows a video signal waveform (Vin); this is inverted the videointo the TV sync separator circuit in FIG. 10, and is coupled toresistor R_(o) (where R_(o) ≈0) of FIG. 10. FIG. 11b shows the effect ofthe coupling capacitor and resistor R_(b). Note at Vb the video signalis ramping up towards the sync tip level. (This is a result of the RCtime constant of resistor Rb and capacitor C since Rb>>Ro.)

FIG. 11c shows narrowed horizontal sync pulses. The action of resistorR_(o) (where R_(o) now is medium resistance i.e. 200 to 1500 ohms),capacitor C, resistor R_(b) and transistor Q1 cause clipping action ofthe narrowed sync tip. Because the sync widths are narrower, capacitor Cis not charged up sufficiently and causes more sync clipping. Recallthat the charging of capacitor C is related to both the amplitude of thesync pulse and its pulse width, i.e. Vc is proportional to (sync pulsewidth) multiplied by (sync amplitude). The lower the voltage Vc the morethe sync clipping action. FIG. 11d shows this result at point in FIG. 10Vb.

FIG. 11e shows an attenuated video source signal from an illegal copywith narrowed sync pulses where "A" indicates the presence of thechecker pulses. The sync separator responds by clipping the sync pulsescompletely and as a result, parts of the video toward the end of lineare interpreted as new sync pulses. FIG. 11f shows this. The syncseparator (inverter) transistor Q1 turns on during the clipped portionof video.

FIG. 11g shows that by slicing parts of the video, the leading edge ofsync is rendered unstable. This leading edge instability of the syncseparator causes the TV to display an unstable image (i.e., shaking sideto side). As shown by the arrows, the resulting unstable horizontal syncpulses are caused by sync narrowing or checker pulses.

FIG. 11h shows what the output of the TV sync separator would have beenfor FIG. 11d, which is a full level TV signal with narrowed sync. Thusthe signal of FIG. 11d poses no playability problems to a TV set. Onlywhen the signal of FIG. 11d is added to a copy protection signal and anillegal copy is made do playability problems become evident on the TVset, because the illegal copy results in an attenuated signal.

FIG. 11i shows with a full unattenuated TV signal that if selected linesnear the end of a video field or after the vertical sync pulses (i.e.NTSC lines 256-259, lines 10-12) are narrowed with varying amplitude(i.e. switching from about blanking level to about 10-100 IRE), the syncseparator transistor Q1 will start ramping up to slice into the picturearea, i.e. "ZZ" of FIG. 11j. This causes a wider pulse in the "ZZ" area,but not wide enough to cause a vertical sync pulse.

FIG. 11k shows the sync separator output of the waveform of FIG. 11j. Ifthis waveform is to be accompanied by anticopy protection signals, theillegal copy will provide an attenuated signal to the TV sync separatoras in FIG. 11l. FIG. 11l is an attenuated TV signal due to illegalcopying with narrowed syncs accompanying the end of field lines.

FIG. 11m shows the ramping action at point V_(b) via resistor Rb andcapacitor C. The corresponding output of the sync separator shows at "y"a new (spurious) broad (vertical sync) pulse. This new pseudo-verticalsync pulse has been created when the narrowed horizontal sync pulses arewith the end of field lines at blanking level. When the narrowedhorizontal sync pulses are accompanied with 10 to 100 IRE, the TV syncseparator only outputs narrow horizontal rate sync pulses, and no newbroad pulses. This is because the 10 to 100 IRE levels are ignoredentirely by the sync separator. By the switching in and out of blankingand greater than 10 IRE unit signals, the sync separator sees normalvertical sync sometimes followed by a spurious early or late verticalsync pulse (see FIG. 11n). These spurious early and/or late verticalpulses then cause the TV to jitter up and down when playing back anillegal copy.

In some cases to get the same effect as above one can:

Narrow selected sync pulses to about zero, i.e. eliminate horizontalsync pulse so as to make TV sync separator to make spurious verticalsync pulse.

Reposition a few sync pulses with greater than 63.5 μs periods to causethe sync separator to malfunction and make a new spurious vertical syncpulse. This causes the ramping action of some sync separators to causespurious vertical pulses.

FIG. 11o shows a video signal which is free of spurious vertical syncpulses due to a video signal being above blanking, i.e. greater thanabout 10 IRE units in the area of the narrowed pulses. Thus if the levelof the video signal is high enough relative to blanking level, thepresence of narrowed horizontal sync pulses fails to generate a spuriousvertical sync pulse.

As shown in the sync pulse narrowing circuit of FIG. 12a, the videoinput signal (possibly already carrying the basic copy protectionpulses) is input to terminal 160 where it is supplied to sync separator162 and also to video adder 164. Sync separator 162 outputs separatedhorizontal sync (H sync) and vertical sync signals to line selector gate166 which selects for instance lines 10 to 250 of each video field. Theseparated H sync pulses are also provided to one-shot circuit OS10 whichin response outputs a signal of about 2 μs duration to AND gate U12, theother input of which is a line select signal indicating selected lines10 to 250 from gate 166. In response, AND gate U12 outputs a signalrepresenting a portion of H sync on each of these lines 10 to 250, whichis scaled by amplifier 174. The output of scaling amplifier 174 issummed back into the original video signal at adder 164, the output ofwhich is supplied to video out terminal 180.

FIG. 12b shows a representation of the waveform at point Q of FIG. 12a(the conventional H sync signal with color burst), and the signal at Rwhich is the output of scaling amplifier 174. The summed result of Q andR ("video out" at lower part of FIG. 12b) is seen at the video outterminal 180, which is a shortened H sync pulse with color burst.

Another circuit to perform sync narrowing with extended color burstenvelope (extended burst is necessary to ensure color lock for TV setsif narrowed H syncs cause a color lock problem) is describedhereinafter. FIG. 13a, 13b show a circuit for introducing narrowedhorizontal sync pulses throughout the active video field. Within thisactive field, an EPROM data output determines which lines get narrowedfurther. For example, this EPROM output (EPD1) can allow for lines20-250 to have a 3.7 μs sync replaced pulse width, while lines 251-262have a 2.0 μs sync replaced pulse width. Other combinations are possibledependent on programming EPD1 in EPROM U9. Also, another output fromEPROM U9 can cause sync suppression in lines (i.e., lines 255 and/or257) or so, before the location of the EOF pulses (this is done via ANDgate U10 and EPD2 from EPROM U9). Repositioned horizontal sync narrowedsync is also possible after sync suppression in normal HBI is done.

Input video carrying any combinations of: the basic anticopy process,end of field pulses, and checker process or normal RS170 type video isDC sync restored by video amplifier A1 to OV (equal to blanking level).Amplifier A1 outputs into sync separator circuit U2 which in turnoutputs composite sync and a vertical pulse between 1 μs and 20 μs. Togenerate a burst gate to lock input video's burst to circuit 2015, caremust be taken not to generate a burst gate pulse when pseudo sync pulsesare present (i.e., if input video has the basic anticopy process). Thus,one shot U3 takes composite (and pseudo) sync and one shots anon-retriggerable pulse of about 45 μs, long enough to ignore equalizingand vertical 2H pulses in the vertical blanking interval and also thepseudo sync pulses that may be present (usually in the first 32 μs ofthe TV lines 10-20). One shot U10 delays the leading edge of input videosync by 5 μs and triggers one shot U11, a 2 μs one shot to be coincidentwith the input video's color burst.

Amplifier A1 drive a chroma bandpass filter amplifier A91 to input intoburst phaselock loop circuit 2105. The output of PLL circuit 2105 is nowa continuous wave subcarrier locked in phase with the input video'scolor burst. PLL Circuit 2011 adjusts the regenerated subcarrier phaseto be correct at amplifier A5 output. Frame sync pulse from syncseparator U2 resets address counter U8 for EPROM U9. Counter U8 isincremented by a horizontal rate pulse from amplifier A3. EPROM U9outputs each data line that contain particular TV lines high or low inthe active field.

One of the advantages of the circuit of FIGS. 13a and 13b is that theregenerated narrowed sync can be placed anywhere in the horizontalblanking interval (HBI). This becomes advantageous especially if the newnarrowed sync can start 1 μs in advance (before) input video'shorizontal sync. With a 1 μs advance in new narrowed horizontal sync andthe PPS pulse, the horizontal instability with an illegal copy havingthe basic anticopy process results in 1 μs more in horizontal jitter. Byadvancing the narrowed H sync pulse, a greater time distance existsbetween the narrowed H sync pulse and the PPS, yielding proportionallygreater instability when an illegal copy is played back.

To generate an advance narrowed H sync, the output of one shot U2 is a45 μs pulse coincident with the leading edge of input sync is "squared"up via 32 μs one shot U4. The filter including components R1, L1 and C1bandpass filters the output of one shot U4 into a 15.734 KHz sine wave.

By adjusting inductor L1, a sinewave in advance (or behind) of inputvideo's H sync is produced. Comparator A3 converts this sinewave intopulses whose edges are leading or lagging the video input's leading syncedge. The "tracking" ability of filter R1, L1, C1 (with a Q of 4) togenerate waveforms synchronous to the input video is, in general, betterthan most horizontal PLL's when the video input is from a VCR. Theoutput of amplifier A3 then goes to 14 μs one shot U5, to generate anHBI gate signal to replace old (input) sync and burst with new narrowedsync and extended burst.

One shot U6 sets a nominal narrowed sync delay of 0.5 μs from thebeginning of the input video HBI (of one shot U5's leading edge) and oneshot U7 triggers off a new narrowed sync pulse. Components R2, R3 and Q1form a switch to narrow the pulse further by shorting out transistor Q1(emitter to collector) and via command of EPD1 (i.e., for lines 251-262each field EPD1 is low, and high elsewhere). The output of one shot U7is then pulses of 3.7 μs from lines 20 to 250 and pulses of 2 μs from251 to 262. Triggering off the trailing edge of one shot U7 is one shotU12, the output of which is the extended burst gate which (about 5.5 μspulse width).

The output of one shot U12 gates a color burst from circuit 2011 viaswitch SW22, and the band pass filter (3.58 Mhz) amplifier A4 shapes theextended burst envelope from switch SW22 output and couples to summingamplifier A5, via extended burst amplitude adjustment resistor R10.Narrowed H sync from one shot U7 is "anded" via gate U13 with signalEPD2 which is generally high, except for the few lines on which narrowedsync is to be suppressed, which enhances the end of field pulses. Theoutput of gate U13 sums into amplifier A5 via narrowed sync amplitudecontrol resistor R8. The output amplifier of A5 is then narrowed syncplus extended color burst. Switch SW25 switches the output of amplifierA5 via AND gate U14 through OR gate U20, which switches amplifier A5output during the HBI via one shot U5 output and EPD3, (active fieldlocation pulses i.e., lines 20-262).

Buffer amplifier A22 then outputs video from input with new narrowed Hsync and extended color burst. To gate in a repositioned sync pulse(EOFRSP) in the end of field location, one shot U16 is 10 μs to 40 μs inlength from the leading sync edge of input video. Gate U16 couples togate U17 a 2 μs to 4 μs wide pulse that is delayed about 10 μs to 40 μsfrom the input video's leading sync edge. The output of gate U16 isenabled via AND gate U18 and EPD4 from EPROM U9. Signal EPD4 is thenhigh at certain lines at the end of the field after sync suppression isactivated via EPD2. Gate U16 drives summing amplifier A5 via EOFRSPamplitude adjustment resistor R85. Gate U16 also turns switch SW25 onduring activation of EOFRSP through OR gate U20 to insert therepositioned sync pulse (EOFRSP). Thus the output of amplifier A2 hasinput video, narrowed sync and possibly 1 or 2 lines of suppressed sync(no sync) or/and a few lines of repositioned narrowed H-sync.

The sync pulse narrowing is effective even if not all horizontal syncpulses in a video signal are so narrowed. It has been determined thateven a relatively small number of narrowed horizontal sync pulsesprovide a spurious vertical retrace. For instance, three to sixconsecutive video lines with a narrowed horizontal sync pulse areadequate for this purpose. It is preferred to group together thenarrowed horizontal sync pulses in consecutive (or at least relativelyclose together) lines to generate the spurious vertical retrace.

Other circuitry for sync pulse narrowing, in the context of removal ofcopy-protection signals, is disclosed in U.S. Pat. No. 5,157,510, RonQuan et al., and U.S. Pat. No. 5,194,965, Ron Quan et al., bothincorporated by reference.

FIGS. 14a and 14b show block diagrams of two apparatuses for combiningthe above described sync pulse narrowing with the earlier describedprior art copy protection process and horizontal and vertical signalmodifications.

FIG. 14a shows the first such apparatus, with program video supplied tocircuitry block 204, for adding the prior art copy protection signalsincluding the added AGC and pseudo-sync pulses. The next block 206(shown in detail in FIG. 6a) adds (1) the checker pattern and (2) thevertical rate signal modifications to the end of each of selectedfields. Then the sync pulse narrowing circuitry block 208 (shown invarying detail in FIGS. 12a and FIGS. 13a and 13b) further modifies thevideo signal, which is output at terminal 209, for instance, to a masterduplicator VCR in a video cassette duplication facility. It has alsobeen observed that the prior art basic anticopy process was improved byjust adding in conjunction the sync narrowing process.

Alternatively, in FIG. 14b the input program video signal is firstsubject to the sync pulse narrowing circuitry block 208, and to the copyprotect and checker pattern and vertical rate signal modificationcircuitry blocks 204, 206 (shown here combined into one block) and hencesupplied to output terminal 210.

It is to be understood that other apparatuses may also provide thedisclosed video signal modifications, i.e. the checker pattern, end offield vertical pattern, sync narrowing, and equivalents thereof.

Method and Circuit for Removal of Video Copy Protection SignalModifications

Given an anticopy process signal including at least AGC and pseudo-syncpulses as described above and/or sync narrowing, and/or end of line"checker" pulses, and/or end of field pseudo-vertical sync pulses, amethod and circuit for defeating these is described hereinafter.

For the AGC and pseudo-sync pulses, Ryan, U.S. Pat. No. 4,695,901 andQuan U.S. Pat. No. 5,157,510 both incorporated by reference, disclosemethods and apparatus for defeating (removal or attenuation of) theseadded pulses. Ryan, U.S. Pat. No. 4,695,901 discloses only the removalor attenuation of pseudo-sync and AGC pulses, and does not disclose thedefeat of sync pulse narrowing, end of field pseudo vertical syncpulses, or end of line (checker) pulses. Processing amplifiers as arewell known in the art can remove sync pulse narrowing with regeneratedsync, but processing amplifiers do not defeat the end of line checkerpulses or end of field pseudo-vertical sync pulses.

It is not taught in the prior art how to defeat these copy protectionvertical and checker signals. Merely blanking them out can still causeresidual anticopy signal enhancements to survive when an illegal copy ismade. The reason is that blanking these signals to blanking level alonein the presence of pseudo-sync and AGC pulses will cause an attenuatedvideo signal to be input into a TV set when an illegal copy is made.This attenuated signal then has, for instance, end of field lines atblanking level and can cause pseudo-vertical sync pulses in thissituation. This is true especially if narrowed horizontal sync pulsesare still present.

On the other hand, if only the narrowed sync pulses are restored tonormal sync width, the other two copy protection enhancement signals(checker and vertical) are still effective.

Thus the following methods defeat the above disclosed anticopy processenhancements:

1) The end of line (checker modification) copy protection signals arereplaced with a signal at least about 20% of peak white, or a levelshifting signal of at least 20% of peak white is added to the end ofline signal. The signal replacement or adding may be to a portion of thechecker signal so as to defeat the process. By "portion" is meant thepart of the end of line pulse to be "neutralized" or part of all thelines of video that has the end of line pulses.

2) The end of field (vertical) copy protection pulses are replaced witha signal that is at least about 20% of peak white for a period of atleast around 32 μsec per line; alternatively a level shifting signal ofat least about 20% of peak white is added to the vertical pulses for atleast around 32 μsec on enough lines (i.e. 7 of 9, 5 of 7, 2 of 3) todefeat the anticopy process.

It is to be understood that the 20% of peak white level referred to herewith respect to the vertical and checker pulses has been experimentallydetermined to be a typical minimum value needed to produce the intendedeffect of defeating the video signal enhancements, and that a higherlevel signal (such as 30% or more) would accomplish the purpose evenmore thoroughly.

3) Most (5% or more) of the narrowed horizontal sync pulses are widenedso as to defeat the sync narrowing process, i.e. if sync is narrowed to3.0 μsec, a widened sync pulse to 4.0 μsec may be adequate to defeat thesync narrowing process, and without the need to replace the narrowedsync with RS170 standard horizontal sync pulses. (Note that 4.7 μsec isspecified as the horizontal sync pulse width for the RS170 standard.)

4) A widened sync pulse width encroaching into the end of line (checker)pulses can be used to defeat both the checker and sync narrowingprocesses. Care must take to assure that the flyback pulse of the TV setstill triggers color burst, because widening the sync pulse to includepart of the checker pulses can cause the TV set's flyback pulse totrigger prematurely.

5) A horizontal sync and colorburst with adequate sync and burst widthrepositioned into the checker pulses can defeat both the sync narrowingand the checker processes, without causing the TV set's flyback signalto trigger incorrectly the TV set's color burst signal.

The vertical pulses will have the effect of vertical sync signals on aTV set if reduced video amplitude is present. Most TV sets or VCRs needabout 30 μs to trigger the vertical sync filter to output a verticalpulse. Thus, by modifying the vertical pulses such that even if residualpseudo-vertical pulses are of less duration than for instance 20 μs,then no pseudo-vertical sync pulses are output from the vertical syncfilter.

Sufficient defeat of the checker pulses results if the "low" state ofthe checker pulse is shortened so as to cause a narrowed horizontal syncpulse not to be detected by the TV set's or VCR's sync separator. Thisavoids the effect of the checker pattern when playing back in an illegalcopy.

FIG. 15 shows a two step circuit and method for removing all theabove-described anticopy protection signals. A video signal containingAGC, pseudo-sync, checker, vertical pulses, and narrowed horizontal-syncpulses is first input on terminal 228 into the circuitry 230 asdisclosed in Ryan, U.S. Pat. No. 4,695,901 or Quan, U.S. Pat. No.5,157,510 to defeat the effects of the AGC pulses and pseudo-syncpulses. Second, the output signal from circuitry 230 is input into theenhancement remover 234 which defeats the checker and vertical pulses,and also defeats sync narrowing and any residual AGC pulse orpseudo-sync pulses in the horizontal blanking interval. The video andsignal at terminal 236 is thus free of all effects of copy protectionsignals.

In this embodiment, the checker and vertical pulses are defeated(ideally) by replacing these pulses with pulses having an amplitude ofabout 20% of peak white pulses, or by adding a level shifting signalhaving an amplitude of about 20% of peak white. The checker pulses canalso be defeated by substituting in a wide horizontal sync signal,thereby replacing the checker pulses. This defeats the checker pulsesand widens the horizontal sync pulse to defeat the sync narrowingprocess. Finally, if the HBI (horizontal blanking interval) is replacedby new horizontal sync and color burst, then the sync narrowing and anyAGC pulse and/or pseudo-sync pulse in the active field are defeated.

Also in this embodiment, narrowing the black level duration of thechecker and vertical pulses results in a viewable copy. Also, any AGCpulses following a normal horizontal sync pulse can be defeated byadding a negative level shifting pulse to counter the elevated colorburst (AGC pulse) or by sync and burst replacement. A circuit foraccomplishing this is described hereinafter. In FIG. 16, showing detailsof block 234 of FIG. 15, an enhanced anticopy protected signal is inputto amplifier A10 having gain K (i.e. K is equal to 2). The output ofamplifier A10 is coupled to capacitor C1, diode D1, and resistor R1,which together are a DC sync restoration circuit. Resistor R2, capacitorC2, and capacitor C1 form a color subcarrier frequency notch filter sothat comparator All can separate sync properly. Voltage reference Vb1sets the slice point to cause comparator A101 to function as a syncseparator. The output of comparator All is then fed to a low pass filterincluding components resistor R3, inductor L1 and capacitor C3 torecover a vertical rate pulse. Comparator A12 with reference input levelV_(b2) is a vertical sync separator.

Because this video signal can be from a VCR, certain sync separators,i.e. the LM 1881, produce incorrect frame pulses with VCR outputs. So togenerate a frame pulse, one shot U1 outputs a pulse that ends slightlyshort of six lines from the beginning of the first vertical sync pulse.One shot U2 outputs pulse having a width of about 25 μs.

Then AND gate U7 logically "ands" the output of inverter U6 with that ofone-shot U2 to generate a pulse occurring every two fields or eachframe. Only in one field is output from U2 and U6 high. Gate U7's outputis the signal (FID) gate which triggers (see FIG. 17) one shot U8 havinga pulse duration of 11/2 fields. With D flip flop U9 and with the outputof one shot U8 connected to the D input of flip flop U9 and verticalsync as the clock input for flip flop U9, a frame rate square wave isproduced with its rising and falling edges coincident with the firstvertical sync (broad) pulse of the incoming video signal. One shot U10with counter circuit U11 and horizontal rate pulse from horizontal PLLU4 generates signals on a 10 bit address bus B10 that counts 525 states.EPROM U12 is addressed by 10 bit bus B10, and dependent on how EPROM U12is programmed, EPROM U12's output lines carry the following signals:

1) Active field location (AF) (high states from line 22 to line 262).

2) End of field location (EOFL) (high states from line 254 to 262).

In FIG. 16, PLL circuit U4 and one shot U5 are a horizontal rate PLLcircuit such that PLL circuit U4's output is in advance of the leadingedge of video horizontal sync by about 3 μs. This is done by one shotU5, which delays PLL U4's output by about 3 μs. The output of one shotU5 is fed back to a phase detector input of PLL U4. Since the edges ofboth detector inputs of PLL U4 must match, PLL U4's output must then bein advance of the leading sync edge amplifier (comparator) A101. PLL U4also ignores any pulses other than horizontal rate. Thus vertical pulsesand others are ignored by PLL U4.

Furthermore, one shot U3 develops a burst gate pulse (BG) of incomingvideo by timing off the trailing edge of sync from comparator All.

FIG. 18 shows a level shifting circuit defeating the checker andvertical pulses. Amplifiers A20, A21 form a summing amplifier. Signalssupplied to this summing amplifier are via resistor R100 for video, viaresistor R101 for end of line pulses, and via resistor R102 for end offield pulses. By using the advance horizontal pulse (AHP) which startsat the same time as each of the checker pulses, a pulse of about 1.5 μsduration is timed off the AHP using the active field pulse AF from EPROMU12. AND gate U13 generates a logic high pulse (EOLD) at the end of eachline during the active field. This pulse from gate U13 then is added tothe video, which causes the checker pulses never to come down toblanking level. Instead, the checker pulses now have a minimum 20% ofpeak white level. This defeats the end of line checker pulses becauseunder the circumstance of an attenuated video signal, the checker pulsesdo not go down in video level enough to cause a sync separator to"accidentally" trigger.

Similar results are achieved for the vertical pulses where one shot U16generates an active horizontal line pulse of about 49 μs duration (aminimum of 35 μsec) via the AHP into one shot U15 for a pulse that endsat the HBI. One shot U16 then triggers off one shot U15 (14 μsec pulseduration) to form an active line pulse. This active horizontal linepulse is and'd by gate U150 with the end of field location (EOFL) pulsevia EPROM U12. The EPROM U12 EOFL pulses send a high logic signal at theend of the field during the horizontal active line via gate U150. Thishigh logic level from gate U150 output is then added to the video signalby resistor R102 to ensure that the vertical pulses are at a minimumlevel of 20% of peak white. With the vertical pulses having a level ofat least 20% of peak white, under attenuated video circumstances, thesenew end of field lines will not cause a pseudo-vertical sync. The outputof amplifier A21 then contains defeat mechanisms for both checker andend of field pulses. To defeat the sync narrowing process, the output ofamplifier A21 is coupled to capacitor C12, capacitor C13, diode D10,diode D11, and resistor R12, which form a DC sync tip amplifier. VoltageVD2 is set to have 0 volts DC at blanking level into amplifier A22.

By using AHP again, one shot U17 and one shot U18 generate a new widenedsync pulse. Components R17, C18, C3, C19, R18 and R19 are a low passfilter for finite rise time sync. Voltage V_(b3) is set to establishblanking level for the "high" state of new widened sync. One shots U19and U20 with AND gate U21 are the control logic to reinsert the newwider horizontal sync pulse during the active field. The outputs of oneshots U19 and U20 are slightly delayed from U17 and U18 to accommodatethe delay in the lowpass filter including components R17, C18, L3, etc.Electronic switch SW1 thus switches in the widened sync and outputsvideo out to amplifier A23. The right hand portion of FIG. 18 within thedotted line is the sync replacement and output circuitry S50.

FIG. 19 shows a circuit to be used in conjunction with that of FIG. 16that replaces the checker pulses with new widened horizontal sync pulsesand a new color burst to follow these new widened horizontal syncpulses. Also the vertical modification pulses are defeated by levelshifting via source signal EOFD (from FIG. 18) into resistors R412 andR411.

Input video is fed to a chroma band pass filter including componentsR299, C400, L400 and C401 into burst regenerator U40 (part numberCA1398) which is a burst to continuous wave subcarrier (3.58 mhz)regenerator; crystal Y40 is a 3.58 mHz crystal. The output of burstregenerator U40 is filtered via a band pass filter (3.58 mHz pass,including components R300, L401 and C402) and buffered by amplifier A40.Electronic switch SW40 gates in new color burst via one shot U43. Oneshot U43 is triggered by the trailing edge of the regenerated widenedsync of one shot U41. One shot U40 is a 0.5 μs delay to establish ahorizontal sync front porch "breezeway". Regenerated sync from one shotU41 output is filtered and level shifted via components R307, L403,C404, R305, R306 and voltage V400. Amplifier A42 buffers this levelshifted widened regenerated sync to sum in with color burst via resistorR304 and amplifier A43. Electronic switch SW41 gates in during theactive field (via AND gate U44 and the AF source signal from EPROM U12)new widened sync and new burst during the HBI. (The new widened sync andnew burst also defeats any anticopy video signals with active field AGCpulses in the HBI, i.e. raised back porch pulses). Amplifier A44 buffersand outputs new video with defeated anticopy signals including narrowedsync, checker pulses, vertical pulses.

FIG. 20 shows a circuit for "level shifting" by multiplying a non-zerovoltage to a higher voltage. End of line defeat signal EOLD and end offield defeat signal EOFD are used for level shifting in FIG. 16 generatea control voltage to raise the gain of voltage controlled amplifier(VCA) U50 (part number MC1494) during the presence of checker pulses andvertical modification pulses in the copy protected signal. The video isDC restored so that sync tip is at 0 V, which means low states of thechecker and vertical modification pulses are above 0 V (typical from 0.3V to 0.5 V). Components C201, R201, D10, D20, C200, R200 and A49 formthis DC restored video signal. The output of VCA U50 then has aequivalent level shifted or amplified anticopy signal well aboveblanking level to defeat the anticopy enhancements. Amplifier A50buffers the output signals from VCA U49 into the narrowed sync pulsedefeat circuit of FIG. 16.

FIGS. 21, 22, and 23 show alternatives to defeat the checker andvertical anticopy signals by switching circuitry.

FIG. 21 shows that (for the DC restored video of FIG. 16) during thechecker and vertical pulses, control voltages coincident with thesepulses switch in (under control of the EOLD and EOFD signals) a 20% ofpeak white signal V₁₀, overriding the anticopy pulses by electronicswitches respectively SW199 and SW198. The finite driving impedance ofthe video signal allows for this (resistor R200 providing the impedanceof about 2000 ohms). The video signal is then amplified by amplifierA501, and processed by the sync replacement and output circuitry S50 ofFIG. 18, before being outputted at terminal 506.

FIGS. 22 and 23 show alternative switching circuits to that of FIG. 21to defeat checker and vertical pulses. (Sync replacement and outputcircuitry S50 is not shown in FIGS. 22, 23 but is present as in FIG.21). In FIG. 22, the DC restored video input signal is again applied viaresistor R201 to amplifier A54, with override switches SW198, SW199under control respectively of the EOLD and EOFD pulses switching involtages V1, V2, each of which is a DC or DC offset AC signal greaterthan or equal to 20% of peak white. The circuit of FIG. 23 is similar tothat of FIG. 22, except that switches SW198, SW199 are located seriallydirectly in the video signal path and use conventional replacement meansto overcome the checker and end of field pulses. In certain cases merelyblanking the checker and EOF pulses (blanking level V₁ =V₂ =V₁₀) may besufficient in a viewable copy to defeat the effects of checker or EOFpulses.

Apparatus To Defeat Horizontal And Vertical Enhancements By SyncWidening.

FIG. 24a shows a circuit with copy protected video with vertical (EOF)and checker (EOL) enhancements provided to input buffer amplifier A60for defeat of the checker and vertical enhancements by sync pulsewidening. The output of amplifier A60 is coupled to sync separator U61.The composite sync output of sync separator U60 is fed to one shot U61to eliminate 2H pulses in composite sync. The output of one shot U64 isfed to PLL oscillator U65. The PLL's U65 frequency for N=910 is 14.31818MHz, equal to N times the horizontal line frequency (Nf_(H)). By usingNf_(H) to clock counter U68 and f_(H) to reset it, EPROM U69 receives a11 bit address bus from counter U68. EPROM U69 now can output horizontalpixel locations (as programmed into EPROM U69). The outputs of EPROM U69contain the horizontal timing for:

Pre-pseudo sync location

Sync widening location

New Burst gate location

Pseudo sync locations for EOF pulse

The output of sync separator U61 also has a field ID (Frame) pulse whichresets a 525 state counter U63. State counter U63 is clocked by ahorizontal frequency pulse by the PLL U65 and divided by N counter U607.EPROM U66 then has the horizontal line locations within the active TVfield. For example: in EPROM U66, D_(o) =lines 22-253 and D₁ =lines254-262, the location of the vertical modification pulses.

Referring to FIG. 24b, logic gates U610 to U614 utilize the data outputsof EPROMs U69 and U66 for the following:

1) Pre-pseudo sync and sync widening locations are gated through signalDO for pre-pseudo sync and widening sync (H) to be on lines 22-253. Theoutput of gate U613 does this.

2) A sync widening only on lines 254 to 262 plus added pseudo syncpulses only on lines 254 to 262; U612 output accomplishes this. OR gateU614 combines the outputs of gates V612 and U613 and ORs these with D3H,the new burst gate signal. The output of gate U614 controls switch Sw600to insert:

Pre-pseudo sync (Lines 22 to 253)

H Sync widening (Lines 22 to 262 new burst gate)

3) The new burst gate signal from signal D3H also, and D3 the activefield pulse, gates the signal fsc cw via amplifier A65 AND gate U615.The output of gate U615 is color subcarrier which is on only whensignals D3H and D3 are high. Variable resistor R607 sets the new burstlevel, and capacitor C607, inductor L607 and resistor R604 filter thenew burst envelope. U616 combines only the pre-pseudo sync, pseudo sync,widened sync pulses and sums into inverting summing amplifier viaamplitude control R602 and R603. Summing amplifier A67 then has:pre-pseudo sync, widened H sync, new burst, and pseudo sync, and switchSW205 switches the output of amplifier A67 during the coincident times.

FIGS. 25a to 25h show waveforms as labelled at various points in thecircuit of FIGS. 24a, 24b.

FIG. 24C shows a typical PLL circuit for oscillator U65 of FIG. 24acausing a varactor tuning diode LC oscillator 252 with a set-reset phasedetector U70 and low pass filter (less than 1 KHz) including resistorR700 and capacitor C700, and a D.C. amplifier 250 including amplifierA70, and the associated components R702, C703, R703, R704 and voltagereference V_(bb).

Another Method Of Defeating Checker And Vertical Enhancements

Another circuit for defeating the checker and vertical pulses is shownin FIG. 26, where since switch SW100 is of low resistance, essentiallythe checker and vertical modification pulses are attenuated and/or levelshifted or replaced by a voltage that is the average voltage (due toswitch averaging circuit 260) in the high-low states of the end of line(checker) pulses and the end of field (vertical modification) pulses.For example, if the checker and vertical modification pulses have highstates of 30 IRE and low states of 0 IRE, the capacitor C1 will chargeto a voltage to approximately ##EQU1## Because switch SW100 is on duringthe checker period at the end of the line and on during the end of fieldpulses due to gate U304, during these times the capacitor C1 voltageoverrides the input video signal with approximately a 15 IRE level,enough to defeat the enhanced anti-copy signals.

In FIG. 26, enhanced anticopy video signals are fed to input amplifierA1 which outputs into sync separator circuit 258 which outputs a shortduration frame pulse (i.e. 10 μs) to reset memory address counters incircuit 260. Meanwhile, composite sync (including possibly pseudo syncpulses from the prior art basic anticopy process) is fed to a horizontalphaselock loop circuit (PLL) U303. The output of PLL U303 is then ahorizontal frequency pulse which starts about 2 μs before the frontporch of input video. The EPROM of circuit 260 has outputs correlatingto the checker and end of field pulses line locations in the TV field.One shot U100 outputs a pulse coincident with the checker locationwithin the horizontal line, while one-shots U200 and U300 form a pulsesuch that the output of U300 has a pulse coincident with the end offield pulses within the horizontal line. The locations of checker andend of field pulses are gated through gates U202 and U203 and "or'd" viagate U304 to output pulses coincident in time with checker (EOL) and endof field pulses of the input video. Switch SW103 turns on during thesecoincident times to attenuate via resistor RS and average out (viacapacitor C1) the enhanced copy protected signals, to output a moreviewable signal from amplifier A2.

Another defeat method is to switch in either or both peak negative orpeak positive clipper circuits during the presence of the checker (EOL)and vertical modification (EOF) pulses, as shown in FIG. 27. The inputcopy protected video is clamped by buffer amplifier A6. EOF and EOLlocations are identified by the circuit and input to OR gate U305. DiodeD1 positively clips the checker (high) gray pattern and verticalmodification high gray pulses to render a more copiable recording. DiodeD2 negatively clips the (low) black level of both the EOL and EOF pulsesto a gray level to render a copiable recording via switches SW101,SW102. Amplifier A7 buffers the actions of switches SW101, SW102 tooutput a copiable video signal.

A third defeat method is to sense the checker pulses and verticalmodification pulses and add inverse pulses. Since the check pattern runsup or/and down, and the vertical modification pulses run up and down,the circuit of FIG. 28 senses and nulls out EOF and EOL pulses.

Although nulling may be less effective because reduces the checker orend of field pulses to about blanking level (0 IRE), nulling can in somecases cause a more viewable picture. (Recall ideally the checker and endof field pulses should be above about 20 IRE for total defeat). Nullingthus causes the Hi and Lo states of the checkers and end of field pulsesto go to a low state (0 IRE). FIG. 28 shows a hulling circuit. Videofrom amplifier A1 output of FIG. 26 is DC restored to have blankinglevel about 0 V via components C15, D15, Vb15, R15 and A246 feed intoswitch SW124 that passes the checker and end of field pulses via "or"gate U247. Gate U247 has checker and end of field locations "identified"via gates U202 and U203 from FIG. 26. Inverter A82 inverts the signalfrom switch SW124 and sums in this inverted checker/end of field pulsevia resistor R2 back to incoming video (via resistor R1) to null out thechecker and end of field pulses. (Resistors R1 and R1 have equalvalues). Amplifier A209 buffers this video signal with nulled outchecker and end of field pulses. (Resistor R6 keeps a DC bias to groundfor inverting amplifier A82).

Yet another defeat method (for use against the EOL and EOF pulses) is toattenuate peak active video from 100% to 80% (by about 20%), and alsoincrease the sync amplitude (by about 50%) as shown in the waveforms ofFIGS. 29a and 29b. This requires an increase of composite sync from 40IRE to about 60 IRE. This can also defeat pseudo-sync pulses of the kinddisclosed in U.S. Pat. No. 4,631,603 because the pseudo sync pulsestherein are 40 IRE. With prolonged composite sync pulses, syncseparation circuits tend to separate only the large sync pulses andignore the smaller amplitude ones. Thus the pulse pairs (pseudo-syncplus AGC pulse) will not be sensed. FIG. 29a shows the original inputwaveform for one video line. FIG. 29b shows the video line waveformmodified for both the checker and vertical modification pulses.

FIG. 29b shows a resultant waveform with modified sync amplitudes to beabout 50% over the standard video with checker and end of field pulses.Since the composite sync signals are larger, the attenuation by theillegal copy will generally not be enough to cause the checker and endof field pulses to be of any effect when viewing an illegal copy.Because the horizontal and vertical sync are modified to be much larger,the TV or VCR sync separator will not mistrigger.

FIG. 30 shows a circuit to provide the waveform of FIG. 29b. Enhancedanticopy protected signals are input to an amplifier A84 with gain of0.8. These input signals are also clamped and have blanking level equalto 0 V. Sync separator circuit 302 outputs composite sync CS to analogswitch SW210 and 300 attenuator. Attenuator circuit 300 attenuates thetypical logic level of composite sync (i.e. 5 V peak to peak) and viaoffset voltage -V. Attenuator circuit 300 outputs a regeneratedcomposite sync of 60 IRE (with 0 IRE equal to 0 V) to -60 IRE levels.Switch SW210 then switches in this new regenerated sync to output viaamplifier A505 a waveform like that of FIG. 29b.

Another defeat method as shown in the circuit of FIG. 31 is to track andhold the active video line to replace the checker pulse with the lastvalue of active video before the beginning of the EOL pulses.

By using from the circuit of FIG. 26 A1 output and U202 output alongwith the circuit of FIG. 31, it is possible to defeat the checkers bytracking and holding. This method is similar to reinserting a knownvoltage during the time of checker pulses. Since most program materialis above 0 IRE (especially in NTSC where black level is 7.5 IRE),tracking and holding the video results in a level generally greater than7.5 IRE, which is enough to defeat the checkers when this level isre-inserted in the checker location.

Amplifier A90 receives input from amplifier A1 of FIG. 26. Amplifier A90has a delay of 100 ns to 200 ns (via delay lines or low pass filters) sothat the pulse from gate U202 tracks and holds video 100 ns to 200 nsjust before the checker pulses. Switch 310 is on at all times and is offduring the checker pulses' times. Thus, amplifier A92 output essentiallyis video transparent until switch 300 turns off and capacitor C107 fillsin for 2 μs the last program pixel (greater than approximately 7.75 IRE)during the checker pulse time.

Another defeat method as shown in the waveforms of FIGS. 32a, 32b is toadd a high frequency signal to the EOF and EOL pulses so as toeffectively level shift by the average DC level of the high frequencysignal. FIG. 32a shows in the upper waveform the video input signalincluding the EOF pulse, and in the lower waveform the high frequencylevel shifting signal having a frequency of 0.1 to 5 MHz. The lowerwaveform of FIG. 32a can be applied to the checker pulses as well (at afrequency of 3 MHz for example). The resulting VCR recorded signal isshown in FIG. 32b, with the wavy portion having a frequency 3 MHz. Theadded high frequency signal causes the VCR to respond only to theaverage DC level, thereby level shifting the high and low states of theEOF and/or EOL pulses so as to be ineffective.

Since these above described enhancements are dependent on the TV setcircuitry as well, as shown in FIG. 33 these "anti-enhancement" (defeat)circuits 322 can be connected between a playback VCR 320 and the TV 324to ensure a more viewable image of the illegal tape copy, using ifneeded RF modulator 326.

Pre-sync Pulses Defeating Horizontal And Vertical Modifications

The following describes how wider than normal sync pulse replacement(i.e. normal sync of 4.7 μs vs. wider sync of 6 μs to 10 μs) negatesvertical modification (end of field) and checker (end of line) pulsesrespectively.

In the sync separators used in TV sets as shown in prior art FIG. 10,the composite sync pulses charge up the input sync separator couplingcapacitor C. The slice threshold is a function of the average chargetime per TV line. The greater the charge time, the further the "slice"point is away from the blanking level. Also, because the slice point isramping toward blanking level due to resistor R_(b) and capacitor C, async pulse preceding the end of line pulses causes the ramping to betemporarily slowed down as to avoid slicing during the end of linepulses or end of field pulses.

FIG. 34a shows the TV sync separator's response to a TV signal (invertedvideo representation) including the basic anticopy process of U.S. Pat.No. 4,631,603 plus just the checker anti-copy enhancement. The TV syncseparator slice point 328 clearly falls into the "A" regions, (thechecker regions) and thus causes on/off pre-sync pulses that result in achecker pattern on the TV set picture.

The waveform of FIG. 34b shows the result of wider than normal syncpulses. The resulting TV sync separator slice point 330 clearly neverfalls into the "A" checker region, and thus the TV does not experience achecker pattern. The color burst waveform may need to be added in the"CBX" region throughout the horizontal sync region to ensure color lockof the TV or VCR.

FIGS. 35a, 35b show respectively a normal video horizontal sync pulseand a widened horizontal sync pulse with regenerated color burst (CB)added to the second half of the widened sync pulse, and the color burstadded after the trailing edge of this widened horizontal sync pulse. Theadded regenerated color burst is to ensure that TV sets still have acolor burst to lock onto, whether the TV triggers color burst off theleading or trailing edge of sync.

The regenerated color burst is not necessary for the location of thevertical modification pulses sync; these happen at the bottom of the TVfield which is generally not viewed.

The following explains how adding sync pulses and pre-sync pulsesnegates the effects of (defeats) the end of field and end of linepulses:

By adding sync and pre-sync pulses, the TV's sync separator couplingcapacitor C charges up more. Thus the slice point of the sync separatorcircuit moves away from blanking level, avoiding the end of line pulsesand end of field pulses.

The waveform of FIG. 34c shows video with added pre-sync pulses; the TVor VCR sync separator slice point 5331 does not go into the end of linelocation. Similar results are shown for vertical modification pulseswith gating in pseudo sync pulses in FIG. 36c. FIG. 36a shows verticalmodification pulse "B" with normal H sync width and TV sync separatorslice point 336. Note that the slice point 336 of the TV sync separatorslices into the vertical modification pulse B. FIG. 36b shows thecorresponding waveform with widened H sync width, having TV syncseparator slice point 338 that avoid slicing into the "B" region(vertical modification pulses).

Post-sync Pulses Additional Horizontal Modifications

FIG. 37 shows a circuit to add post-pseudo sync pulses to enhanceanticopy effectiveness (i.e., further degrade viewability) when anillegal copy is made with the above described basic anticopy process ofU.S. Pat. No. 04,631,603.

Video with the basic anti-copy process plus other above-describedenhancements is input to resistor R9. Amplifier A1 buffers input videoand couples it via capacitor C1 into the sync separator U6. The verticalsync output of sync separator U6 resets a 12 bit counter U1. Counter U1is clocked by horizontal sync to a PLL U2 that is locked to compositesync. EPROM U3 selects on which lines the post-pseudo sync (PPS) mayappear. A pseudo-random distribution of post-pseudo sync may be used, asselected by EPROM U3. Signal DO (an output of EPROM U3) inhibits oneshot OS3 accordingly. The burst gate signal from sync separator U6 isinverted and low pass filtered by capacitor C2 and resistor R2. VoltageVgen sums in a signal (i.e., 300 Hz triangle wave form) into capacitorC2. This causes a time varying threshold difference into one shot OS3and thus causes a position change. The output of one shot OS3 is a fixedpulse (i.e., 1.5 μs duration) with pulse position modulation for exampleof ±1 μs. The output of one shot OS3 blanks out any video to blankinglevel via switch SW1 and adds a pulse by variable R7 to generate a postpseudo-sync pulse. Summing amplifier A3 inverts the output pulse of oneshot OS3 to maintain the correct shape of the added post pseudo-syncpulse. FIGS. 38a to 38e show waveforms at various points in the circuitof FIG. 37, as labelled. The amplitude of the post pseudo sync may beamplitude modulated via VGen2 and voltage controlled amplifier A41 whichis a multiplying amplifier. The output of amplifier A41 varies inamplitude according to VGen2, being 0 V when the post pseudo sync pulseis off.

Defeat Method And Apparatus For Post Sync Enhancement

FIG. 39a shows another defeat circuit for use with "video in" containingthe above-described post pseudo-sync pulses (PPS) coupled to syncseparator U1 by capacitor C1. That is, the circuit of FIG. 39a reducesor removes the effect of the PPS pulses, rendering the video signalrecordable. Sync separator U1 feeds composite sync into a horizontalphase lock loop U2. The H PLL U2 is phased to begin in the area of thepost pseudo sync pulse (after burst). One shot U5 triggers off H PLL U2to generate a pulse that contains the post pseudo-sync pulse. Verticalsync from one shot sync separator U1 triggers sync separator U4 togenerate a pulse from extending TV from line 4 to line 21, and one shotU4 triggers one shot U5 to generate an active field pulse from lines 22to 262. The output of one shot U5 (which is the complement of thevertical blanking interval) gates AND gate U10 so that the output ofgate U10 is on only during the active TV field.

Thus the output of gate U10 indicates locations of the post pseudo-syncpulses during the active field. FIGS. 39b, 39c, 39d show waveformslabelled for three points in the circuit of FIG. 39a.

FIG. 40a shows the output signal of gate U10 of FIG. 39a used to defeatthe post pseudo-sync pulses by generating a pulse (PPSD) coincident tothe PPS signal and level shifting via analog multiplier U6 (part number1494). Multiplier U6 increases or decreases the gain during the time thepost pseudo-sync defeat pulse U10 output is present. When signal VID1 isprovided to multiplier U6, the sync tip is 0 V at VID1. By increasingthe gain at the right time, the result is waveform Z of FIG. 40b. Byusing signal VID2 into multiplier U6 instead of VID1 and using theoutput of gate U10, multiplexer U6 is reconfigured to attenuate with thepositive going pulse of U10 output and the gain is reduced at the righttime to produce waveform Y of FIG. 40c, defeating the process.

By using signal VID2 into an analog switch SW220 of the circuit of FIG.40d, gate U10's output controls switch SW220 to insert a referencevoltage. If VR is 0 V, waveform X of FIG. 40e results in a blanked-outpost pseudo-sync. If VR is at sync tip voltage (i.e., -40 IRE), theresult is waveform U of FIG. 40f which creates an additional H syncpulse of fixed amplitude and position. This causes most TV sets to havea static horizontal picture offset and none of the "wariness" the postpseudo-sync pulse would otherwise cause.

By summing the output of gate U10 into amplifier A6 in the circuit ofFIG. 40g, level shifting occurs to defeat the post pseudo-sync pulse,the waveform for which is also shown in FIG. 40b. FIG. 40h identifiesthe position of the PPS and level shifting.

Finally, narrowing the post pseudo-sync pulse to defeat its effect isdone by slicing sync. As shown in FIG. 41a, amplifier A7 receives videoVID2 with a notched-out color subcarrier due to a notch filter R100,inductor L100, and capacitor C100. Amplifier A7 output slices bothnormal sync and post pseudo-sync by setting V_(bb2) to approximately-10. By using AND gate U7, and the PPS from gate U10 (FIG. 39a), gate U7outputs a pulse that is inverted but identical to the original postpseudo sync pulse at logic levels. One shot U8 is timed for greater than90% of the pulse period of the post pseudo-sync pulse and then controlsswitch SW224 to truncate the leading edge of the post pseudo-sync pulseby greater than 90%. The result is the waveform as seen in FIG. 4lb"VIDEO OUT DD" which shows a very narrow post pseudo-sync pulse, so asto cause no response in any video device (i.e., VCR or TV set). Also bysumming the output of gate U7 (FIG. 41a) into amplifier A6 of FIG. 40gvia resistor R6, this results in an output that is level shifted pastpseudo sync, as seen in FIG. 40h. This method can partially or fullycancel the post pseudo sync pulse amplitudes as well, which results inattenuated post pseudo sync.

Method And Apparatus For Reducing Effects Of Basic Anticopy ProcessSignals

The following describes a method and apparatus in which the basicanti-copy process signals consisting of pseudo sync and AGC (i.e. basicanticopy process) added pulses (as described above) are reduced ineffectiveness, without altering these added pulses. Unlike the abovedescribed previous methods for altering the added pulses via amplitudeattenuation, level shifting or pulse narrowing to offset the addedpulses' effect, the present method reduces the effects of added pulsesby further adding other pulses that counteract the gain reduction causedby the AGC and pseudo-sync pulses.

U.S. Pat. No. 4,631,603 describes how the AGC circuit in a VCR measuresthe incoming video signal amplitude using a sync and back porch sample.By adding extra sync pulses with a very high level back porch, gainreduction occurs. Because the AGC circuit in a VCR continuously samplesthe sync amplitude (via a sync sample and a back porch sample) thepresent method negates some of the anticopy signals by moving all theback porch levels from blanking, to below blanking level (i.e. about -20IRE units for NTSC video). It is also possible with the present methodto add extra pseudo-sync pulses in the area at the bottom of the TVfield (end of field) where anticopy signals containing AGC andpseudo-sync pulses are not present. These "extra" pseudo-sync pulses arefollowed by pulses below blanking level.

Referring to FIG. 42a, the basic anti-copy protected video ("video in")is coupled to a sync separator U2 (part number LM 1881 or equivalent).The composite sync from sync separator U2 triggers the trailing edge ofsync to a 3 μs one shot U3.

Vertical sync from sync separator U2 triggers one shots U4 and U5 toform an active field pulse provided as an input to AND gate U1 which"ands" the active field pulse and the output of one-shot U3. The outputof gate U1 is then a 3 μs backporch pulse during the active TV field.(Alternatively, one-shots U4 and U5 are not necessary and one-shot U3output goes directly to resistor R6, eliminating U1, U4 and U5).Resistor R6 is a negative summing resistor that subtracts a level fromthe back porch of the video input. Input amplifier A0 buffers the videoinput and couples to capacitor C3, diode D1, resistor R3 and voltage Vbthat forms a sync tip DC restoration circuit. The output of feedbackamplifier A3 is supplied to resistor R7; this output has a lowered backporch. (See FIGS. 43a to 43g showing signals at various locations inFIG. 42a, as labelled).

The circuit of FIG. 42b receives the video out 1 signal from resistor R7of the circuit of FIG. 42a and replaces the last 10 or 11 lines of eachTV field with TV lines containing pseudo sync pulses paired withsubsequent AGC pulses below blanking level, i.e. -10 to -30 IRE. Thevideo from the node of diode D1 of FIG. 42a contains video that is DCrestored to 0 volts for 0 IRE blanking level. Amplifier A2 of FIG. 42bamplifies this video and couples it to horizontal lock oscillator U11(using pin 1 of oscillator CA 31541, where the sync tip from amplifierA2 is at 7 V). The output of oscillator U11 is a 32H phase lock loop andoutputs a signal of about 503 KHz frequency. This 503 KHz output signalis amplified for logic levels by amplifier A2 and input to binarydivider U10.

Summing amplifier A4 outputs a square wave signal of approximately 2 μson and 2 μs off of amplitude -20 IRE to -40 IRE. Voltage Vbb andresistor R9 set the proper DC offset voltage, whereas resistors R10 andR11 set the proper amplitude. In FIG. 42a one-shot U6 generates anactive line pulse of 32 μs duration from the beginning of the activehorizontal line; one shots U7 and U8 are triggered by the vertical syncpulse to turn high during the last 11 lines of the active TV field. ANDgate U9 of FIG. 42b thus gates in a 4 μs period square wave of levels of-20 IRE to -40 IRE during the last 11 horizontal active lines of the TVfield (where the pseudo sync and AGC pulses are not generally located).Amplifier A5 and resistor R12 output a modified anticopy signal withlowered backporch pulses and new pseudo-sync and lowered negative AGCpulses.

The modified video signal provided by the circuit of FIGS. 42a and 42bcauses the AGC amplifier in a VCR to measure incorrectly. As a resultbased on its measurements of the pseudo sync pulses (and with loweredback porch) paired with AGC pulses of reduced level, it appears to theVCR that a low level video signal is present, and thus the VCR increasesthe gain of its AGC amplifier. This offsets the reduction of the gain inthe AGC VCR amplifier via the basic anticopy process. The addedpseudo-sync pulses in the EOF locations each has in one embodiment atleast about 2 μsec of blanking level (0 IRE) following the trailing edgeof each added pseudo-sync pulse to defeat the EOF (vertical)modification. This is accomplished by a switch or waveform replacementcircuit as described variously above. This is useful if the high stateof the EOF modification has an amplitude greater than 10 to 20 IPE. Inthe absence of the blanking level under these conditions, the EOFmodification effect may be reduced but the prior art basic anticopyprocess effect increased, thus increasing the EOL modification andpreventing defeat of the overall anticopy process.

The above description of the invention is illustrative and not limiting;other modifications in accordance with the invention will be apparent toone of ordinary skill in the art in light of this disclosure and areintended to fall within the scope of the appended claims.

What is claimed is:
 1. A method of defeating the effects of a videoanti-copy process that adds pulses to blanking intervals of a videosignal, comprising replacing a back porch portion of the video signalhaving an amplitude at blanking level with a signal having an amplitudebelow the blanking level.
 2. The method of claim 1, wherein theamplitude below the blanking level is about -20 IRE units.
 3. The methodof claim 1, further comprising the steps of:generating a plurality ofnegative-going pulses; and adding the plurality of negative-going pulsesto about the last ten active lines of at least some fields of the videosignal.
 4. The method of claim 3, further comprising the step ofmodifying a portion of the video signal following each addednegative-going pulse to be at a blanking level of the video signal for apredetermined period.
 5. The method of claim 1, wherein the step ofreplacing includes adding a negative level shifting pulse to the backporch portion of the video signal.
 6. A method of defeating a video copyprotection process that adds paired negative and positive going pulsesto blanking intervals of a video signal, the method thereby enablingrecording a viewable copy of the video signal, comprising the stepsof:determining a particular portion of at least some video lines of thevideo signal, the added pulses being present in the particular portion;and reducing a level of the particular portion to below a blanking levelof the video signal.
 7. The method of claim 6, wherein the particularportion includes a backporch of each of the video lines.
 8. The methodof claim 6, wherein the level is lower than about -20 IRE units.
 9. Themethod of claim 6, further comprising the steps of:determining a portionof each field of the video signal containing none of the added pulses;generating a plurality of negative-going pulses; generating a pluralityof positive-going pulses having a level of about -10 to -30 IRE; andadding the plurality of the generated negative-going and positive-goingpulses to the determined portion of each field.
 10. An apparatus fordefeat of an anti-copy process that adds paired negative-going andpositive-going pulses to blanking intervals of a video signal,comprising:means for determining a back porch portion of the videosignal, the back porch having an amplitude of a blanking level of thevideo signal; and means for replacing the back porch portion with asignal having an amplitude below the blanking level.
 11. The apparatusof claim 10, further comprising:a generator for generating a pluralityof negative-going pulses; and means for adding the plurality ofnegative-going pulses to about the last ten lines of at least somefields of the video signal.
 12. An apparatus for defeat of a video copyprotection process that adds pulses to blanking intervals of a videosignal, comprising:a generator for generating a signal below a blankinglevel of the video signal; timing circuitry for determining durations ofparticular portions of at least some lines of the video signal, theadded pulses being present in the particular portions; and an addingcircuit for adding the generated signal to the video signals at thedetermined duration.